diff --git a/backend/auspost.c b/backend/auspost.c
index b3225686..5d251aa4 100644
--- a/backend/auspost.c
+++ b/backend/auspost.c
@@ -1,8 +1,7 @@
 /* auspost.c - Handles Australia Post 4-State Barcode */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2008 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -29,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 static const char GDSET[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz #";
 #define GDSET_F (IS_NUM_F | IS_UPR_F | IS_LWR_F | IS_SPC_F | IS_HSH_F)
@@ -124,11 +123,11 @@ INTERNAL int auspost(struct zint_symbol *symbol, unsigned char source[], int len
     /* Do all of the length checking first to avoid stack smashing */
     if (symbol->symbology == BARCODE_AUSPOST) {
         if (length != 8 && length != 13 && length != 16 && length != 18 && length != 23) {
-            strcpy(symbol->errtxt, "401: Auspost input is wrong length (8, 13, 16, 18 or 23 characters only)");
+            strcpy(symbol->errtxt, "401: Input wrong length (8, 13, 16, 18 or 23 characters only)");
             return ZINT_ERROR_TOO_LONG;
         }
     } else if (length > 8) {
-        strcpy(symbol->errtxt, "403: Auspost input is too long (8 character maximum)");
+        strcpy(symbol->errtxt, "403: Input too long (8 character maximum)");
         return ZINT_ERROR_TOO_LONG;
     }
 
@@ -280,3 +279,5 @@ INTERNAL int auspost(struct zint_symbol *symbol, unsigned char source[], int len
 
     return error_number;
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/big5.h b/backend/big5.h
index a12e98c0..58ece87a 100644
--- a/backend/big5.h
+++ b/backend/big5.h
@@ -1,6 +1,5 @@
-/*  big5.h - tables for Unicode to Big5,
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/OTHER/BIG5.TXT" */
+/*  big5.h - tables for Unicode to Big5, generated by "backend/tools/gen_eci_mb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/OTHER/BIG5.TXT" */
 /*
     libzint - the open source barcode library
     Copyright (C) 2021-2022 Robin Stuart <rstuart114@gmail.com>
diff --git a/backend/codablock.c b/backend/codablock.c
index 940b52c4..041c57a8 100644
--- a/backend/codablock.c
+++ b/backend/codablock.c
@@ -1,8 +1,7 @@
 /* codablock.c - Handles Codablock-F and Codablock-E */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2016 - 2021 Harald Oehlmann
+    Copyright (C) 2016-2022 Harald Oehlmann
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -29,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include <stdio.h>
 #include <math.h>
@@ -81,7 +80,7 @@ static int GetPossibleCharacterSet(unsigned char C)
 {
     if (C<='\x1f')      /* Control chars */
         return CodeA;
-    if (C>='0' && C<='9')
+    if (z_isdigit(C))
         return ZTNum;   /* ZTNum=CodeA+CodeB+CodeC */
     if (C==aFNC1) /* FNC1s (GS1) not used */
         return ZTFNC1;  /* ZTFNC1=CodeA+CodeB+CodeC+CodeFNC1 */ /* Not reached */
@@ -965,3 +964,5 @@ INTERNAL int codablockf(struct zint_symbol *symbol, unsigned char source[], int
 
     return error_number;
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/code1.c b/backend/code1.c
index 057e6b7a..a196b595 100644
--- a/backend/code1.c
+++ b/backend/code1.c
@@ -1,5 +1,4 @@
 /* code1.c - USS Code One */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
@@ -29,6 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include "common.h"
 #include "code1.h"
@@ -101,7 +101,7 @@ static void c1_spigot(struct zint_symbol *symbol, const int row_no) {
 
 /* Is basic (non-shifted) C40? */
 static int c1_isc40(const unsigned char input) {
-    if ((input >= '0' && input <= '9') || (input >= 'A' && input <= 'Z') || input == ' ') {
+    if (z_isdigit(input) || z_isupper(input) || input == ' ') {
         return 1;
     }
     return 0;
@@ -109,7 +109,7 @@ static int c1_isc40(const unsigned char input) {
 
 /* Is basic (non-shifted) TEXT? */
 static int c1_istext(const unsigned char input) {
-    if ((input >= '0' && input <= '9') || (input >= 'a' && input <= 'z') || input == ' ') {
+    if (z_isdigit(input) || z_islower(input) || input == ' ') {
         return 1;
     }
     return 0;
@@ -201,7 +201,7 @@ static int c1_look_ahead_test(const unsigned char source[], const int length, co
         const int is_extended = c & 0x80;
 
         /* Step L */
-        if ((c >= '0') && (c <= '9')) {
+        if (z_isdigit(c)) {
             ascii_count += C1_MULT_1_DIV_2; /* Step L1 */
         } else {
             if (is_extended) {
@@ -328,7 +328,7 @@ static int c1_is_last_single_ascii(const unsigned char source[], const int lengt
 static void c1_set_num_digits(const unsigned char source[], const int length, int num_digits[]) {
     int i;
     for (i = length - 1; i >= 0; i--) {
-        if (source[i] >= '0' && source[i] <= '9') {
+        if (z_isdigit(source[i])) {
             num_digits[i] = num_digits[i + 1] + 1;
         }
     }
@@ -743,9 +743,9 @@ static int c1_encode(struct zint_symbol *symbol, unsigned char source[], int len
 
                 if (debug_print) printf("EDI ");
 
-                if ((source[sp] >= '0') && (source[sp] <= '9')) {
+                if (z_isdigit(source[sp])) {
                     cte_buffer[cte_p++] = source[sp] - '0' + 4;
-                } else if ((source[sp] >= 'A') && (source[sp] <= 'Z')) {
+                } else if (z_isupper(source[sp])) {
                     cte_buffer[cte_p++] = source[sp] - 'A' + 14;
                 } else {
                     cte_buffer[cte_p++] = posn(edi_nonalphanum_chars, source[sp]);
diff --git a/backend/code49.c b/backend/code49.c
index 48350546..28ba4c97 100644
--- a/backend/code49.c
+++ b/backend/code49.c
@@ -1,8 +1,7 @@
 /* code49.c - Handles Code 49 */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2009 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -29,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include <stdio.h>
 #include "common.h"
@@ -82,9 +81,9 @@ INTERNAL int code49(struct zint_symbol *symbol, unsigned char source[], int leng
     i = 0;
     h = d - intermediate;
     do {
-        if ((intermediate[i] >= '0') && (intermediate[i] <= '9')) {
+        if (z_isdigit(intermediate[i])) {
             /* Numeric data */
-            for (j = 0; (intermediate[i + j] >= '0') && (intermediate[i + j] <= '9'); j++);
+            for (j = 0; z_isdigit(intermediate[i + j]); j++);
             if (j >= 5) {
                 /* Use Numeric Encodation Method */
                 int block_count, c;
@@ -389,3 +388,5 @@ INTERNAL int code49(struct zint_symbol *symbol, unsigned char source[], int leng
 
     return error_number;
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/common.c b/backend/common.c
index ba3f1efe..1af5d9f7 100644
--- a/backend/common.c
+++ b/backend/common.c
@@ -1,5 +1,4 @@
 /* common.c - Contains functions needed for a number of barcodes */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
@@ -29,6 +28,8 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
+
 #include <assert.h>
 #ifdef ZINT_TEST
 #include <stdio.h>
@@ -40,7 +41,7 @@
 
 /* Converts a character 0-9, A-F to its equivalent integer value */
 INTERNAL int ctoi(const char source) {
-    if ((source >= '0') && (source <= '9'))
+    if (z_isdigit(source))
         return (source - '0');
     if ((source >= 'A') && (source <= 'F'))
         return (source - 'A' + 10);
@@ -64,7 +65,7 @@ INTERNAL int to_int(const unsigned char source[], const int length) {
     int i;
 
     for (i = 0; i < length; i++) {
-        if (source[i] < '0' || source[i] > '9') {
+        if (!z_isdigit(source[i])) {
             return -1;
         }
         val *= 10;
@@ -79,7 +80,7 @@ INTERNAL void to_upper(unsigned char source[], const int length) {
     int i;
 
     for (i = 0; i < length; i++) {
-        if ((source[i] >= 'a') && (source[i] <= 'z')) {
+        if (z_islower(source[i])) {
             source[i] = (source[i] - 'a') + 'A';
         }
     }
@@ -353,8 +354,7 @@ INTERNAL int is_fixed_ratio(const int symbology) {
 
 /* Whether next two characters are digits */
 INTERNAL int is_twodigits(const unsigned char source[], const int length, const int position) {
-    if ((position + 1 < length) && (source[position] >= '0') && (source[position] <= '9')
-            && (source[position + 1] >= '0') && (source[position + 1] <= '9')) {
+    if ((position + 1 < length) && z_isdigit(source[position]) && z_isdigit(source[position + 1])) {
         return 1;
     }
 
diff --git a/backend/common.h b/backend/common.h
index 7aafe634..b4527e3c 100644
--- a/backend/common.h
+++ b/backend/common.h
@@ -1,5 +1,4 @@
 /* common.h - Header for all common functions in common.c */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
@@ -70,6 +69,11 @@
 /* The most commonly used set */
 #define NEON_F      IS_NUM_F /* NEON "0123456789" */
 
+/* Simple versions of <cctype> functions with no dependence on locale */
+#define z_isdigit(c) ((c) <= '9' && (c) >= '0')
+#define z_isupper(c) ((c) >= 'A' && (c) <= 'Z')
+#define z_islower(c) ((c) >= 'a' && (c) <= 'z')
+
 #include "zint.h"
 #include "zintconfig.h"
 #include <stdlib.h>
diff --git a/backend/composite.c b/backend/composite.c
index 26d23975..017768cf 100644
--- a/backend/composite.c
+++ b/backend/composite.c
@@ -979,10 +979,10 @@ static int cc_binary_string(struct zint_symbol *symbol, const unsigned char sour
 
         for (i = 0; i < ninety_len; i++) {
 
-            if ((ninety[i] >= 'A') && (ninety[i] <= 'Z')) {
+            if (z_isupper(ninety[i])) {
                 /* Character is alphabetic */
                 alpha += 1;
-            } else if ((ninety[i] >= '0') && (ninety[i] <= '9')) {
+            } else if (z_isdigit(ninety[i])) {
                 /* Character is numeric */
                 numeric += 1;
             } else {
@@ -993,15 +993,16 @@ static int cc_binary_string(struct zint_symbol *symbol, const unsigned char sour
         /* must start with 0, 1, 2 or 3 digits followed by an uppercase character */
         test1 = -1;
         for (i = 3; i >= 0; i--) {
-            if ((ninety[i] >= 'A') && (ninety[i] <= 'Z')) {
+            if (z_isupper(ninety[i])) {
                 test1 = i;
             }
         }
 
         test2 = 0;
         for (i = 0; i < test1; i++) {
-            if (!((ninety[i] >= '0') && (ninety[i] <= '9'))) {
+            if (!z_isdigit(ninety[i])) {
                 test2 = 1;
+                break;
             }
         }
 
@@ -1108,10 +1109,10 @@ static int cc_binary_string(struct zint_symbol *symbol, const unsigned char sour
             if (ai90_mode == 2) {
                 /* Alpha encodation (section 5.3.3) */
                 do {
-                    if ((source[read_posn] >= 'A') && (source[read_posn] <= 'Z')) {
+                    if (z_isupper(source[read_posn])) {
                         bp = bin_append_posn(source[read_posn] - 65, 5, binary_string, bp);
 
-                    } else if ((source[read_posn] >= '0') && (source[read_posn] <= '9')) {
+                    } else if (z_isdigit(source[read_posn])) {
                         bp = bin_append_posn(source[read_posn] + 4, 6, binary_string, bp);
 
                     } else if (source[read_posn] == '[') {
diff --git a/backend/dmatrix.c b/backend/dmatrix.c
index 7c89e213..6e5cb951 100644
--- a/backend/dmatrix.c
+++ b/backend/dmatrix.c
@@ -207,7 +207,7 @@ static int dm_isc40(const unsigned char input) {
     if (input <= '9') {
         return input >= '0' || input == ' ';
     }
-    return input >= 'A' && input <= 'Z';
+    return z_isupper(input);
 }
 
 /* Is basic (non-shifted) TEXT? */
@@ -215,7 +215,7 @@ static int dm_istext(const unsigned char input) {
     if (input <= '9') {
         return input >= '0' || input == ' ';
     }
-    return input >= 'a' && input <= 'z';
+    return z_islower(input);
 }
 
 /* Is basic (non-shifted) C40/TEXT? */
@@ -328,7 +328,7 @@ static int dm_look_ahead_test(const unsigned char source[], const int length, co
         const int is_extended = c & 0x80;
 
         /* ascii ... step (l) */
-        if ((c <= '9') && (c >= '0')) {
+        if (z_isdigit(c)) {
             ascii_count += DM_MULT_1_DIV_2; // (l)(1)
         } else {
             if (is_extended) {
@@ -721,26 +721,22 @@ static int dm_last_ascii(const unsigned char source[], const int length, const i
         if ((source[from] & 0x80) || (source[from + 1] & 0x80)) {
             return 0;
         }
-        if (source[from] <= '9' && source[from] >= '0' && source[from + 1] <= '9' && source[from + 1] >= '0') {
+        if (z_isdigit(source[from]) && z_isdigit(source[from + 1])) {
             return 1;
         }
         return 2;
     }
     if (length - from == 3) {
-        if (source[from] <= '9' && source[from] >= '0'
-                && source[from + 1] <= '9' && source[from + 1] >= '0' && !(source[from + 2] & 0x80)) {
+        if (z_isdigit(source[from]) && z_isdigit(source[from + 1]) && !(source[from + 2] & 0x80)) {
             return 2;
         }
-        if (source[from + 1] <= '9' && source[from + 1] >= '0'
-                && source[from + 2] <= '9' && source[from + 2] >= '0' && !(source[from] & 0x80)) {
+        if (z_isdigit(source[from + 1]) && z_isdigit(source[from + 2]) && !(source[from] & 0x80)) {
             return 2;
         }
         return 0;
     }
-    if (source[from] <= '9' && source[from] >= '0'
-            && source[from + 1] <= '9' && source[from + 1] >= '0'
-            && source[from + 2] <= '9' && source[from + 2] >= '0'
-            && source[from + 3] <= '9' && source[from + 3] >= '0') {
+    if (z_isdigit(source[from]) && z_isdigit(source[from + 1]) && z_isdigit(source[from + 2])
+            && z_isdigit(source[from + 3])) {
         return 2;
     }
     return 0;
@@ -939,8 +935,7 @@ static void dm_addEdges(struct zint_symbol *symbol, const unsigned char source[]
 
         static const int c40text_modes[] = { DM_C40, DM_TEXT };
 
-        if (source[from] <= '9' && source[from] >= '0' && from + 1 < length
-                && source[from + 1] <= '9' && source[from + 1] >= '0') {
+        if (z_isdigit(source[from]) && from + 1 < length && z_isdigit(source[from + 1])) {
             dm_addEdge(symbol, source, length, edges, DM_ASCII, from, 2, previous, 0);
             /* If ASCII vertex, don't bother adding other edges as this will be optimal; suggested by Alex Geller */
             if (previous && previous->mode == DM_ASCII) {
@@ -1191,9 +1186,9 @@ static int dm_minimalenc(struct zint_symbol *symbol, const unsigned char source[
             static const char x12_nonalphanum_chars[] = "\015*> ";
             int value = 0;
 
-            if ((source[sp] >= '0') && (source[sp] <= '9')) {
+            if (z_isdigit(source[sp])) {
                 value = (source[sp] - '0') + 4;
-            } else if ((source[sp] >= 'A') && (source[sp] <= 'Z')) {
+            } else if (z_isupper(source[sp])) {
                 value = (source[sp] - 'A') + 14;
             } else {
                 value = posn(x12_nonalphanum_chars, source[sp]);
@@ -1379,9 +1374,9 @@ static int dm_isoenc(struct zint_symbol *symbol, const unsigned char source[], c
                 static const char x12_nonalphanum_chars[] = "\015*> ";
                 int value = 0;
 
-                if ((source[sp] <= '9') && (source[sp] >= '0')) {
+                if (z_isdigit(source[sp])) {
                     value = (source[sp] - '0') + 4;
-                } else if ((source[sp] >= 'A') && (source[sp] <= 'Z')) {
+                } else if (z_isupper(source[sp])) {
                     value = (source[sp] - 'A') + 14;
                 } else {
                     value = posn(x12_nonalphanum_chars, source[sp]);
diff --git a/backend/dotcode.c b/backend/dotcode.c
index 89dbe931..06b447e8 100644
--- a/backend/dotcode.c
+++ b/backend/dotcode.c
@@ -419,7 +419,7 @@ static int dc_datum_c(const unsigned char source[], const int length, const int
 static int dc_n_digits(const unsigned char source[], const int length, const int position, const int max) {
     int i;
 
-    for (i = position; (i < length) && ((source[i] >= '0') && (source[i] <= '9') && i < position + max); i++);
+    for (i = position; (i < length) && z_isdigit(source[i]) && (i < position + max); i++);
 
     return i - position;
 }
@@ -453,7 +453,7 @@ static int dc_ahead_c(const unsigned char source[], const int length, const int
 /* Annex F.II.F */
 static int dc_try_c(const unsigned char source[], const int length, const int position) {
 
-    if (position < length && source[position] >= '0' && source[position] <= '9') { /* dc_n_digits(position) > 0 */
+    if (position < length && z_isdigit(source[position])) { /* dc_n_digits(position) > 0 */
         const int ahead_c_position = dc_ahead_c(source, length, position);
         if (ahead_c_position > dc_ahead_c(source, length, position + 1)) {
             return ahead_c_position;
@@ -688,7 +688,7 @@ static int dc_encode_message(struct zint_symbol *symbol, const unsigned char sou
             /* Step C3 */
             if (dc_binary(source, length, position)) {
                 /* dc_n_digits(position + 1) > 0 */
-                if (position + 1 < length && source[position + 1] >= '0' && source[position + 1] <= '9') {
+                if (position + 1 < length && z_isdigit(source[position + 1])) {
                     if ((source[position] - 128) < 32) {
                         codeword_array[ap++] = 110; // Upper Shift A
                         codeword_array[ap++] = source[position] - 128 + 64;
diff --git a/backend/eci_sb.h b/backend/eci_sb.h
index 9de5a67a..b5995ec4 100644
--- a/backend/eci_sb.h
+++ b/backend/eci_sb.h
@@ -1,8 +1,8 @@
-/*  eci_sb.h - Extended Channel Interpretations single-byte,
-    generated by "backend/tools/gen_eci_sb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/ISO8859/8859-*.TXT" and
-    "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP125*.TXT" */
-/* libzint - the open source barcode library
+/*  eci_sb.h - Extended Channel Interpretations single-byte, generated by "backend/tools/gen_eci_sb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/ISO8859/8859-*.TXT"
+    and "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP125*.TXT" */
+/*
+    libzint - the open source barcode library
     Copyright (C) 2021-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
diff --git a/backend/gb18030.h b/backend/gb18030.h
index 89acd2f0..3f2779f2 100644
--- a/backend/gb18030.h
+++ b/backend/gb18030.h
@@ -1,6 +1,5 @@
-/*  gb18030.h - tables for Unicode to GB 18030-2005,
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "jdk-1.4.2/GB18030.TXT"
+/*  gb18030.h - tables for Unicode to GB 18030-2005, generated by "backend/tools/gen_eci_mb_h.php"
+    from "jdk-1.4.2/GB18030.TXT"
     (see https://haible.de/bruno/charsets/conversion-tables/GB18030.tar.bz2) */
 /*
     libzint - the open source barcode library
diff --git a/backend/gb2312.h b/backend/gb2312.h
index 2ecb3beb..f5134e97 100644
--- a/backend/gb2312.h
+++ b/backend/gb2312.h
@@ -1,6 +1,5 @@
-/*  gb2312.h - tables for Unicode to GB 2312-1980 (EUC-CN),
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "unicode.org-mappings/EASTASIA/GB/GB2312.TXT"
+/*  gb2312.h - tables for Unicode to GB 2312-1980 (EUC-CN), generated by "backend/tools/gen_eci_mb_h.php"
+    from "unicode.org-mappings/EASTASIA/GB/GB2312.TXT"
     (see https://haible.de/bruno/charsets/conversion-tables/GB2312.tar.bz2) */
 /*
     libzint - the open source barcode library
diff --git a/backend/gbk.h b/backend/gbk.h
index 3b1b9e90..d0cf5c44 100644
--- a/backend/gbk.h
+++ b/backend/gbk.h
@@ -1,6 +1,5 @@
-/*  gbk.h - tables for Unicode to GBK, excluding mappings in GB 2312,
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP936.TXT" */
+/*  gbk.h - tables for Unicode to GBK, excluding mappings in GB 2312, generated by "backend/tools/gen_eci_mb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP936.TXT" */
 /*
     libzint - the open source barcode library
     Copyright (C) 2022 Robin Stuart <rstuart114@gmail.com>
diff --git a/backend/general_field.c b/backend/general_field.c
index cb4cd0b3..49dd5e7d 100644
--- a/backend/general_field.c
+++ b/backend/general_field.c
@@ -1,5 +1,4 @@
 /* general_field.c - Handles general field compaction (GS1 DataBar and composites) */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2019-2022 Robin Stuart <rstuart114@gmail.com>
@@ -29,6 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include "common.h"
 #include "general_field.h"
@@ -39,10 +39,10 @@ static const char isoiec_puncs[] = "!\"%&'()*+,-./:;<=>?_ "; /* Note contains sp
 
 /* Returns type of char at `i`. FNC1 counted as NUMERIC. Returns 0 if invalid char */
 static int general_field_type(const char *general_field, const int i) {
-    if (general_field[i] == '[' || (general_field[i] >= '0' && general_field[i] <= '9')) {
+    if (general_field[i] == '[' || z_isdigit(general_field[i])) {
         return NUMERIC;
     }
-    if ((general_field[i] >= 'A' && general_field[i] <= 'Z') || posn(alphanum_puncs, general_field[i]) != -1) {
+    if (z_isupper(general_field[i]) || posn(alphanum_puncs, general_field[i]) != -1) {
         return ALPHANUMERIC;
     }
     if (is_sane(IS_ISOIEC_F, (const unsigned char *) general_field + i, 1)) {
@@ -150,10 +150,10 @@ INTERNAL int general_field_encode(const char *general_field, const int general_f
                     /* 7.2.5.5.2/5.4.2 d) */
                     bp = bin_append_posn(0, 3, binary_string, bp); /* Numeric latch "000" */
                     mode = NUMERIC;
-                } else if ((general_field[i] >= '0') && (general_field[i] <= '9')) {
+                } else if (z_isdigit(general_field[i])) {
                     bp = bin_append_posn(general_field[i] - 43, 5, binary_string, bp);
                     i++;
-                } else if ((general_field[i] >= 'A') && (general_field[i] <= 'Z')) {
+                } else if (z_isupper(general_field[i])) {
                     bp = bin_append_posn(general_field[i] - 33, 6, binary_string, bp);
                     i++;
                 } else {
@@ -180,13 +180,13 @@ INTERNAL int general_field_encode(const char *general_field, const int general_f
                         /* Note this rule can produce longer bitstreams if most of the alphanumerics are numeric */
                         bp = bin_append_posn(4, 5, binary_string, bp); /* Alphanumeric latch "00100" */
                         mode = ALPHANUMERIC;
-                    } else if ((general_field[i] >= '0') && (general_field[i] <= '9')) {
+                    } else if (z_isdigit(general_field[i])) {
                         bp = bin_append_posn(general_field[i] - 43, 5, binary_string, bp);
                         i++;
-                    } else if ((general_field[i] >= 'A') && (general_field[i] <= 'Z')) {
+                    } else if (z_isupper(general_field[i])) {
                         bp = bin_append_posn(general_field[i] - 1, 7, binary_string, bp);
                         i++;
-                    } else if ((general_field[i] >= 'a') && (general_field[i] <= 'z')) {
+                    } else if (z_islower(general_field[i])) {
                         bp = bin_append_posn(general_field[i] - 7, 7, binary_string, bp);
                         i++;
                     } else {
diff --git a/backend/gridmtx.c b/backend/gridmtx.c
index 0140ca6a..3395d087 100644
--- a/backend/gridmtx.c
+++ b/backend/gridmtx.c
@@ -28,6 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 /* This file implements Grid Matrix as specified in
    AIM Global Document Number AIMD014 Rev. 1.63 Revised 9 Dec 2008 */
@@ -69,7 +70,7 @@ static int gm_in_numeral(const unsigned int ddata[], const int length, const int
        block of three numeric characters) */
     for (i = in_posn, digit_cnt = 0, nondigit = 0, nondigit_posn = 0; i < length && i < in_posn + 4 && digit_cnt < 3;
             i++) {
-        if (ddata[i] >= '0' && ddata[i] <= '9') {
+        if (z_isdigit(ddata[i])) {
             digit_cnt++;
         } else if (posn(gm_numeral_nondigits, (const char) ddata[i]) != -1) {
             if (nondigit) {
@@ -187,11 +188,11 @@ static void gm_define_mode(char *mode, const unsigned int ddata[], const int len
         if (!double_byte) {
             space = ddata[i] == ' ';
             if (!space) {
-                numeric = ddata[i] >= '0' && ddata[i] <= '9';
+                numeric = z_isdigit(ddata[i]);
                 if (!numeric) {
-                    lower = ddata[i] >= 'a' && ddata[i] <= 'z';
+                    lower = z_islower(ddata[i]);
                     if (!lower) {
-                        upper = ddata[i] >= 'A' && ddata[i] <= 'Z';
+                        upper = z_isupper(ddata[i]);
                         if (!upper) {
                             control = ddata[i] < 0x7F; /* Exclude DEL */
                             if (control && i + 1 < length) {
@@ -200,7 +201,7 @@ static void gm_define_mode(char *mode, const unsigned int ddata[], const int len
                         }
                     }
                 } else if (i + 1 < length) {
-                    double_digit = ddata[i + 1] >= '0' && ddata[i + 1] <= '9';
+                    double_digit = z_isdigit(ddata[i + 1]);
                 }
             }
         }
@@ -523,8 +524,7 @@ static int gm_encode(unsigned int ddata[], const int length, char binary[], cons
                 }
                 if (!(done)) {
                     if (sp != (length - 1)) {
-                        if (((ddata[sp] >= '0') && (ddata[sp] <= '9')) &&
-                                ((ddata[sp + 1] >= '0') && (ddata[sp + 1] <= '9'))) {
+                        if (z_isdigit(ddata[sp]) && z_isdigit(ddata[sp + 1])) {
                             /* Two digits */
                             glyph = 8033 + (10 * (ddata[sp] - '0')) + (ddata[sp + 1] - '0');
                             sp++;
@@ -561,7 +561,7 @@ static int gm_encode(unsigned int ddata[], const int length, char binary[], cons
                 numbuf[1] = '0';
                 numbuf[2] = '0';
                 do {
-                    if ((ddata[sp] >= '0') && (ddata[sp] <= '9')) {
+                    if (z_isdigit(ddata[sp])) {
                         numbuf[p] = ddata[sp];
                         p++;
                     } else if (posn(gm_numeral_nondigits, (const char) ddata[sp]) != -1) {
@@ -651,11 +651,11 @@ static int gm_encode(unsigned int ddata[], const int length, char binary[], cons
 
             case GM_MIXED:
                 shift = 1;
-                if ((ddata[sp] >= '0') && (ddata[sp] <= '9')) {
+                if (z_isdigit(ddata[sp])) {
                     shift = 0;
-                } else if ((ddata[sp] >= 'A') && (ddata[sp] <= 'Z')) {
+                } else if (z_isupper(ddata[sp])) {
                     shift = 0;
-                } else if ((ddata[sp] >= 'a') && (ddata[sp] <= 'z')) {
+                } else if (z_islower(ddata[sp])) {
                     shift = 0;
                 } else if (ddata[sp] == ' ') {
                     shift = 0;
@@ -680,7 +680,7 @@ static int gm_encode(unsigned int ddata[], const int length, char binary[], cons
 
             case GM_UPPER:
                 shift = 1;
-                if ((ddata[sp] >= 'A') && (ddata[sp] <= 'Z')) {
+                if (z_isupper(ddata[sp])) {
                     shift = 0;
                 } else if (ddata[sp] == ' ') {
                     shift = 0;
@@ -705,7 +705,7 @@ static int gm_encode(unsigned int ddata[], const int length, char binary[], cons
 
             case GM_LOWER:
                 shift = 1;
-                if ((ddata[sp] >= 'a') && (ddata[sp] <= 'z')) {
+                if (z_islower(ddata[sp])) {
                     shift = 0;
                 } else if (ddata[sp] == ' ') {
                     shift = 0;
diff --git a/backend/gs1.c b/backend/gs1.c
index 112a0bca..12d3ee9f 100644
--- a/backend/gs1.c
+++ b/backend/gs1.c
@@ -1,8 +1,7 @@
 /* gs1.c - Verifies GS1 data */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2009 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -29,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include <stdio.h>
 #ifdef _MSC_VER
@@ -55,7 +54,7 @@ static int numeric(const unsigned char *data, int data_len, int offset, int min,
         const unsigned char *const de = d + (data_len > max ? max : data_len);
 
         for (; d < de; d++) {
-            if (*d < '0' || *d > '9') {
+            if (!z_isdigit(*d)) {
                 *p_err_no = 3;
                 *p_err_posn = d - data + 1;
                 sprintf(err_msg, "Non-numeric character '%c'", *d);
@@ -233,10 +232,10 @@ static int key(const unsigned char *data, int data_len, int offset, int min, int
     if (!length_only && data_len) {
         data += offset;
 
-        if (data[0] < '0' || data[0] > '9' || data[1] < '0' || data[1] > '9') {
+        if (!z_isdigit(data[0]) || !z_isdigit(data[1])) {
             *p_err_no = 3;
-            *p_err_posn = offset + (data[0] < '0' || data[0] > '9' ? 0 : 1) + 1;
-            sprintf(err_msg, "Non-numeric company prefix '%c'", data[0] < '0' || data[0] > '9' ? data[0] : data[1]);
+            *p_err_posn = offset + z_isdigit(data[0]) + 1;
+            sprintf(err_msg, "Non-numeric company prefix '%c'", data[z_isdigit(data[0])]);
             return 0;
         }
     }
@@ -750,7 +749,7 @@ static int iban(const unsigned char *data, int data_len, int offset, int min, in
         int checksum = 0;
         int given_checksum;
 
-        if (d[0] < 'A' || d[0] > 'Z' || d[1] < 'A' || d[1] > 'Z') { /* 1st 2 chars alphabetic country code */
+        if (!z_isupper(d[0]) || !z_isupper(d[1])) { /* 1st 2 chars alphabetic country code */
             *p_err_no = 3;
             *p_err_posn = d - data + 1;
             sprintf(err_msg, "Non-alphabetic IBAN country code '%.2s'", d);
@@ -763,7 +762,7 @@ static int iban(const unsigned char *data, int data_len, int offset, int min, in
             return 0;
         }
         d += 2;
-        if (d[0] < '0' || d[0] > '9' || d[1] < '0' || d[1] > '9') { /* 2nd 2 chars numeric checksum */
+        if (!z_isdigit(d[0]) || !z_isdigit(d[1])) { /* 2nd 2 chars numeric checksum */
             *p_err_no = 3;
             *p_err_posn = d - data + 1;
             sprintf(err_msg, "Non-numeric IBAN checksum '%.2s'", d);
@@ -863,7 +862,7 @@ static const unsigned char *coupon_vli(const unsigned char *data, const int data
         }
         de = d + vli + vli_offset;
         for (; d < de; d++) {
-            if (*d < '0' || *d > '9') {
+            if (!z_isdigit(*d)) {
                 *p_err_no = 3;
                 *p_err_posn = d - data + 1;
                 sprintf(err_msg, "Non-numeric %s '%c'", name, *d);
@@ -1256,7 +1255,7 @@ INTERNAL int gs1_verify(struct zint_symbol *symbol, const unsigned char source[]
             ai_latch = 0;
         } else if (ai_latch) {
             ai_length++;
-            if ((source[i] < '0') || (source[i] > '9')) {
+            if (!z_isdigit(source[i])) {
                 ai_nonnumeric = 1;
             }
         }
@@ -1399,3 +1398,5 @@ INTERNAL char gs1_check_digit(const unsigned char source[], const int length) {
 
     return itoc((10 - (count % 10)) % 10);
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/hanxin.c b/backend/hanxin.c
index 7cc12651..3360d4d0 100644
--- a/backend/hanxin.c
+++ b/backend/hanxin.c
@@ -1,5 +1,5 @@
-/*  hanxin.c - Han Xin Code
-
+/*  hanxin.c - Han Xin Code */
+/*
     libzint - the open source barcode library
     Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
 
@@ -28,6 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 /* This code attempts to implement Han Xin Code according to ISO/IEC 20830:2021
  * (previously ISO/IEC 20830 (draft 2019-10-10) and AIMD-015:2010 (Rev 0.8)) */
@@ -45,15 +46,15 @@
 /* Find which submode to use for a text character */
 static int hx_getsubmode(const unsigned int input) {
 
-    if ((input >= '0') && (input <= '9')) {
+    if (z_isdigit(input)) {
         return 1;
     }
 
-    if ((input >= 'A') && (input <= 'Z')) {
+    if (z_isupper(input)) {
         return 1;
     }
 
-    if ((input >= 'a') && (input <= 'z')) {
+    if (z_islower(input)) {
         return 1;
     }
 
@@ -253,15 +254,15 @@ static int hx_isFourByte(const unsigned int glyph, const unsigned int glyph2) {
 /* Convert Text 1 sub-mode character to encoding value, as given in table 3 */
 static int hx_lookup_text1(const unsigned int input) {
 
-    if ((input >= '0') && (input <= '9')) {
+    if (z_isdigit(input)) {
         return input - '0';
     }
 
-    if ((input >= 'A') && (input <= 'Z')) {
+    if (z_isupper(input)) {
         return input - 'A' + 10;
     }
 
-    if ((input >= 'a') && (input <= 'z')) {
+    if (z_islower(input)) {
         return input - 'a' + 36;
     }
 
@@ -310,7 +311,7 @@ static int hx_in_numeric(const unsigned int ddata[], const int length, const int
     }
 
     /* Attempt to calculate the average 'cost' of using numeric mode in number of bits (times HX_MULT) */
-    for (i = in_posn; i < length && i < in_posn + 4 && ddata[i] >= '0' && ddata[i] <= '9'; i++);
+    for (i = in_posn; i < length && i < in_posn + 4 && z_isdigit(ddata[i]); i++);
 
     digit_cnt = i - in_posn;
 
diff --git a/backend/ksx1001.h b/backend/ksx1001.h
index dfe98c7d..e2987f72 100644
--- a/backend/ksx1001.h
+++ b/backend/ksx1001.h
@@ -1,6 +1,5 @@
-/*  ksx1001.h - tables for Unicode to EUC-KR (KS X 1001),
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/KSC/KSX1001.TXT" */
+/*  ksx1001.h - tables for Unicode to EUC-KR (KS X 1001), generated by "backend/tools/gen_eci_mb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/KSC/KSX1001.TXT" */
 /*
     libzint - the open source barcode library
     Copyright (C) 2021-2022 Robin Stuart <rstuart114@gmail.com>
diff --git a/backend/large.c b/backend/large.c
index 11e40c22..46f026ca 100644
--- a/backend/large.c
+++ b/backend/large.c
@@ -1,5 +1,4 @@
 /* large.c - Handles binary manipulation of large numbers */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
@@ -59,7 +58,7 @@
 INTERNAL void large_load_str_u64(large_int *t, const unsigned char *s, const int length) {
     uint64_t val = 0;
     const unsigned char *const se = s + length;
-    for (; s < se && *s >= '0' && *s <= '9'; s++) {
+    for (; s < se && z_isdigit(*s); s++) {
         val *= 10;
         val += *s - '0';
     }
diff --git a/backend/mailmark.c b/backend/mailmark.c
index f80fb1e1..2a4feb1a 100644
--- a/backend/mailmark.c
+++ b/backend/mailmark.c
@@ -1,8 +1,7 @@
 /* mailmark.c - Royal Mail 4-state Mailmark barcodes */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2008 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -29,7 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 /*
  * Developed in accordance with "Royal Mail Mailmark barcode C encoding and deconding instructions"
@@ -206,7 +205,7 @@ INTERNAL int mailmark(struct zint_symbol *symbol, unsigned char source[], int le
     // Supply Chain ID is 2 digits for barcode C and 6 digits for barcode L
     supply_chain_id = 0;
     for (i = 3; i < (length - 17); i++) {
-        if ((local_source[i] >= '0') && (local_source[i] <= '9')) {
+        if (z_isdigit(local_source[i])) {
             supply_chain_id *= 10;
             supply_chain_id += ctoi(local_source[i]);
         } else {
@@ -218,7 +217,7 @@ INTERNAL int mailmark(struct zint_symbol *symbol, unsigned char source[], int le
     // Item ID is 8 digits
     item_id = 0;
     for (i = length - 17; i < (length - 9); i++) {
-        if ((local_source[i] >= '0') && (local_source[i] <= '9')) {
+        if (z_isdigit(local_source[i])) {
             item_id *= 10;
             item_id += ctoi(local_source[i]);
         } else {
@@ -253,8 +252,8 @@ INTERNAL int mailmark(struct zint_symbol *symbol, unsigned char source[], int le
         } else {
             if (postcode[8] == ' ') {
                 // Types 1, 2 and 6
-                if ((postcode[1] >= '0') && (postcode[1] <= '9')) {
-                    if ((postcode[2] >= '0') && (postcode[2] <= '9')) {
+                if (z_isdigit(postcode[1])) {
+                    if (z_isdigit(postcode[2])) {
                         postcode_type = 6;
                     } else {
                         postcode_type = 1;
@@ -264,7 +263,7 @@ INTERNAL int mailmark(struct zint_symbol *symbol, unsigned char source[], int le
                 }
             } else {
                 // Types 3 and 4
-                if ((postcode[3] >= '0') && (postcode[3] <= '9')) {
+                if (z_isdigit(postcode[3])) {
                     postcode_type = 3;
                 } else {
                     postcode_type = 4;
@@ -510,3 +509,5 @@ INTERNAL int mailmark(struct zint_symbol *symbol, unsigned char source[], int le
 
     return error_number;
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/maxicode.c b/backend/maxicode.c
index d87bd157..2bb2a9c5 100644
--- a/backend/maxicode.c
+++ b/backend/maxicode.c
@@ -1,5 +1,4 @@
 /* maxicode.c - Handles MaxiCode */
-
 /*
     libzint - the open source barcode library
     Copyright (C) 2010-2022 Robin Stuart <rstuart114@gmail.com>
@@ -29,6 +28,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 /* Includes corrections thanks to Monica Swanson @ Source Technologies */
 #include <stdio.h>
@@ -571,7 +571,7 @@ INTERNAL int maxicode(struct zint_symbol *symbol, struct zint_seg segs[], const
         } else {
             mode = 2;
             for (i = 0; i < lp - 6; i++) {
-                if (((symbol->primary[i] < '0') || (symbol->primary[i] > '9')) && (symbol->primary[i] != ' ')) {
+                if (!z_isdigit(symbol->primary[i]) && (symbol->primary[i] != ' ')) {
                     mode = 3;
                     break;
                 }
@@ -615,7 +615,7 @@ INTERNAL int maxicode(struct zint_symbol *symbol, struct zint_seg segs[], const
                     postcode[i] = '\0';
                     postcode_len = i;
                     break;
-                } else if (postcode[i] < '0' || postcode[i] > '9') {
+                } else if (!z_isdigit(postcode[i])) {
                     strcpy(symbol->errtxt, "555: Non-numeric postcode in Primary Message");
                     return ZINT_ERROR_INVALID_DATA;
                 }
diff --git a/backend/pdf417.c b/backend/pdf417.c
index 77edbab1..b796dcd2 100644
--- a/backend/pdf417.c
+++ b/backend/pdf417.c
@@ -1,6 +1,6 @@
 /* pdf417.c - Handles PDF417 stacked symbology */
-
-/*  Zint - A barcode generating program using libpng
+/*
+    libzint - the open source barcode library
     Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
     Portions Copyright (C) 2004 Grandzebu
     Bug Fixes thanks to KL Chin <klchin@users.sourceforge.net>
@@ -30,6 +30,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 /*  This code is adapted from "Code barre PDF 417 / PDF 417 barcode" v2.5.0
     which is Copyright (C) 2004 (Grandzebu).
@@ -99,7 +100,7 @@ static const char pdf_MicroAutosize[56] = {
 /* 866 */
 
 static int pdf_quelmode(const unsigned char codeascii) {
-    if ((codeascii <= '9') && (codeascii >= '0')) {
+    if (z_isdigit(codeascii)) {
         return NUM;
     }
     if (codeascii < 127 && pdf_asciix[codeascii]) {
diff --git a/backend/postal.c b/backend/postal.c
index 89f07535..4e66aca2 100644
--- a/backend/postal.c
+++ b/backend/postal.c
@@ -1,8 +1,7 @@
 /* postal.c - Handles PostNet, PLANET, FIM. RM4SCC and Flattermarken */
-
 /*
     libzint - the open source barcode library
-    Copyright (C) 2008 - 2021 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2008-2022 Robin Stuart <rstuart114@gmail.com>
     Including bug fixes by Bryan Hatton
 
     Redistribution and use in source and binary forms, with or without
@@ -30,7 +29,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
-/* vim: set ts=4 sw=4 et : */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include <stdio.h>
 #ifdef _MSC_VER
@@ -646,7 +645,7 @@ INTERNAL int japanpost(struct zint_symbol *symbol, unsigned char source[], int l
     i = 0;
     inter_posn = 0;
     do {
-        if (((source[i] >= '0') && (source[i] <= '9')) || (source[i] == '-')) {
+        if (z_isdigit(source[i]) || (source[i] == '-')) {
             inter[inter_posn] = source[i];
             inter_posn++;
         } else {
@@ -732,3 +731,5 @@ INTERNAL int japanpost(struct zint_symbol *symbol, unsigned char source[], int l
 
     return error_number;
 }
+
+/* vim: set ts=4 sw=4 et : */
diff --git a/backend/qr.c b/backend/qr.c
index 638f5fd8..5590fb95 100644
--- a/backend/qr.c
+++ b/backend/qr.c
@@ -80,7 +80,7 @@ static int qr_in_numeric(const unsigned int ddata[], const int length, const int
     }
 
     /* Attempt to calculate the average 'cost' of using numeric mode in number of bits (times QR_MULT) */
-    for (i = in_posn; i < length && i < in_posn + 4 && ddata[i] >= '0' && ddata[i] <= '9'; i++);
+    for (i = in_posn; i < length && i < in_posn + 4 && z_isdigit(ddata[i]); i++);
 
     digit_cnt = i - in_posn;
 
@@ -2542,7 +2542,7 @@ INTERNAL int microqr(struct zint_symbol *symbol, unsigned char source[], int len
 
     /* Determine if alpha (excluding numerics), byte or kanji used */
     for (i = 0; i < length && (alpha_used == 0 || byte_or_kanji_used == 0); i++) {
-        if (ddata[i] < '0' || ddata[i] > '9') {
+        if (!z_isdigit(ddata[i])) {
             if (qr_is_alpha(ddata[i], 0 /*gs1*/)) {
                 alpha_used = 1;
             } else {
diff --git a/backend/rss.c b/backend/rss.c
index 7cbb39c5..612ecdde 100644
--- a/backend/rss.c
+++ b/backend/rss.c
@@ -968,7 +968,7 @@ static int dbar_exp_binary_string(struct zint_symbol *symbol, const unsigned cha
     /* Verify that the data to be placed in the compressed data field is all
     numeric data before carrying out compression */
     for (i = 0; i < read_posn; i++) {
-        if ((source[i] < '0') || (source[i] > '9')) {
+        if (!z_isdigit(source[i])) {
             if (source[i] != '[') {
                 /* Something is wrong */
                 strcpy(symbol->errtxt, "385: Invalid character in Compressed Field data (digits only)");
diff --git a/backend/sjis.h b/backend/sjis.h
index 3d3978fe..da3da2bc 100644
--- a/backend/sjis.h
+++ b/backend/sjis.h
@@ -1,6 +1,5 @@
-/*  sjis.h - tables for Unicode to Shift JIS,
-    generated by "backend/tools/gen_eci_mb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/JIS/SHIFTJIS.TXT" */
+/*  sjis.h - tables for Unicode to Shift JIS, generated by "backend/tools/gen_eci_mb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/JIS/SHIFTJIS.TXT" */
 /*
     libzint - the open source barcode library
     Copyright (C) 2009-2022 Robin Stuart <rstuart114@gmail.com>
diff --git a/backend/tests/test_auspost.c b/backend/tests/test_auspost.c
index e21a6029..31395263 100644
--- a/backend/tests/test_auspost.c
+++ b/backend/tests/test_auspost.c
@@ -27,6 +27,7 @@
     OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     SUCH DAMAGE.
  */
+/* SPDX-License-Identifier: BSD-3-Clause */
 
 #include "testcommon.h"
 
@@ -153,17 +154,17 @@ static void test_input(int index, int debug) {
         /*  7*/ { BARCODE_AUSPOST, "12345678ABCDefgh #", 0, 3, 133, "" }, // Length 18
         /*  8*/ { BARCODE_AUSPOST, "12345678901234567890123", 0, 3, 133, "" },
         /*  9*/ { BARCODE_AUSPOST, "1234567890123456789012A", ZINT_ERROR_INVALID_DATA, -1, -1, "Error 406: Invalid character in data (digits only for length 23)" },
-        /* 10*/ { BARCODE_AUSPOST, "1234567", ZINT_ERROR_TOO_LONG, -1, -1, "Error 401: Auspost input is wrong length (8, 13, 16, 18 or 23 characters only)" }, // No leading zeroes added
+        /* 10*/ { BARCODE_AUSPOST, "1234567", ZINT_ERROR_TOO_LONG, -1, -1, "Error 401: Input wrong length (8, 13, 16, 18 or 23 characters only)" }, // No leading zeroes added
         /* 11*/ { BARCODE_AUSREPLY, "12345678", 0, 3, 73, "" },
         /* 12*/ { BARCODE_AUSREPLY, "1234567", 0, 3, 73, "" }, // Leading zeroes added
-        /* 13*/ { BARCODE_AUSREPLY, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Auspost input is too long (8 character maximum)" },
+        /* 13*/ { BARCODE_AUSREPLY, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Input too long (8 character maximum)" },
         /* 14*/ { BARCODE_AUSROUTE, "123456", 0, 3, 73, "" },
         /* 15*/ { BARCODE_AUSROUTE, "12345", 0, 3, 73, "" },
-        /* 16*/ { BARCODE_AUSROUTE, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Auspost input is too long (8 character maximum)" },
+        /* 16*/ { BARCODE_AUSROUTE, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Input too long (8 character maximum)" },
         /* 17*/ { BARCODE_AUSREDIRECT, "1234", 0, 3, 73, "" },
         /* 18*/ { BARCODE_AUSREDIRECT, "123", 0, 3, 73, "" },
         /* 19*/ { BARCODE_AUSREDIRECT, "0", 0, 3, 73, "" },
-        /* 20*/ { BARCODE_AUSREDIRECT, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Auspost input is too long (8 character maximum)" },
+        /* 20*/ { BARCODE_AUSREDIRECT, "123456789", ZINT_ERROR_TOO_LONG, -1, -1, "Error 403: Input too long (8 character maximum)" },
     };
     int data_size = ARRAY_SIZE(data);
     int i, length, ret;
@@ -195,8 +196,10 @@ static void test_input(int index, int debug) {
     testFinish();
 }
 
-// Australia Post Customer Barcoding Technical Specifications (Revised Aug 2012)
+// Australia Post Customer Barcoding Technical Specifications (Revised 3 Aug 2012) "AusPost Tech Specs"
 // https://auspost.com.au/content/dam/auspost_corp/media/documents/customer-barcode-technical-specifications-aug2012.pdf
+// Australia Post A Guide To Printing the 4-State Barcode (Revised 16 March 2012) "AusPost Guide"
+// https://auspost.com.au/content/dam/auspost_corp/media/documents/a-guide-to-printing-the-4state-barcode-v31-mar2012.pdf
 static void test_encode(int index, int generate, int debug) {
 
     struct item {
@@ -210,67 +213,77 @@ static void test_encode(int index, int generate, int debug) {
         char *expected;
     };
     struct item data[] = {
-        /*  0*/ { BARCODE_AUSPOST, "96184209", 0, 3, 73, "Australia Post Customer Barcoding Tech Specs Diagram 1; verified manually against tec-it",
+        /*  0*/ { BARCODE_AUSPOST, "96184209", 0, 3, 73, "AusPost Tech Specs Diagram 1; verified manually against TEC-IT",
                     "1000101010100010001010100000101010001010001000001010000010001000001000100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000100010000010101010001010000010101010001000101010001000100010000010000"
                 },
-        /*  1*/ { BARCODE_AUSPOST, "3221132412345678", 0, 3, 103, "59 Custom 2 N encoding",
+        /*  1*/ { BARCODE_AUSPOST, "39549554", 0, 3, 73, "AusPost Guide Figure 3, same; verified manually against TEC-IT",
+                    "1000101010101010001010001010001010001000101000001000101010001010000000100"
+                    "1010101010101010101010101010101010101010101010101010101010101010101010101"
+                    "0000100010000010001000100000001000100010000000000010001000000000001010000"
+                },
+        /*  2*/ { BARCODE_AUSPOST, "56439111ABA 9", 0, 3, 103, "AusPost Guide Figure 4, same; verified manually against TEC-IT",
+                    "1000100000101000001010101010001010101010101010101010101010101010100000000000001010100010101010000010100"
+                    "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
+                    "0000001000100010101000000010001010001000100010101010100010101010100000101000000010001000101010000000000"
+                },
+        /*  3*/ { BARCODE_AUSPOST, "3221132412345678", 0, 3, 103, "59 Custom 2 N encoding",
                     "1000100000101010100010001010101010101000101010101000101010101000001000100000101000000000001000000000100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000001000100010101010101000100000101010000010001010001000000010101010001010000010001010101000100000000"
                 },
-        /*  2*/ { BARCODE_AUSPOST, "32211324Ab #2", 0, 3, 103, "59 Custom 2 C encoding",
+        /*  4*/ { BARCODE_AUSPOST, "32211324Ab #2", 0, 3, 103, "59 Custom 2 C encoding",
                     "1000100000101010100010001010101010101000101010101010001010100010100000101000100000000010100000100010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000001000100010101010101000100000101010000010101010001010100010000000100000001000101010000010000000000"
                 },
-        /*  3*/ { BARCODE_AUSPOST, "32211324123456789012345", 0, 3, 133, "62 Custom 3 N encoding",
+        /*  5*/ { BARCODE_AUSPOST, "32211324123456789012345", 0, 3, 133, "62 Custom 3 N encoding",
                     "1000001010001010100010001010101010101000101010101000101010101000001000100000001010101010100010101010100000100000100010101010100010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010100010101010101000100000101010000010001010001000000010101010001010001010101000101000100000001000001010000010001010100010000"
                 },
-        /*  4*/ { BARCODE_AUSPOST, "32211324aBCd#F hIz", 0, 3, 133, "62 Custom 3 C encoding",
+        /*  6*/ { BARCODE_AUSPOST, "32211324aBCd#F hIz", 0, 3, 133, "62 Custom 3 C encoding",
                     "1000001010001010100010001010101010101000101010000010101010100010000010100010100010100010000010000000000000100010100010101010000000100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010100010101010101000100000101010000010100010100010101010001010000010001010100000100010101000000000101000001010100000000010000"
                 },
-        /*  5*/ { BARCODE_AUSPOST, "12345678DEGHJKLMNO", 0, 3, 133, "62 Custom 3 C encoding GDSET 1st part",
+        /*  7*/ { BARCODE_AUSPOST, "12345678DEGHJKLMNO", 0, 3, 133, "62 Custom 3 C encoding GDSET 1st part",
                     "1000001010001010100010101010100000100010000010101010101010001010001010101010101010100010101010101010100000001010000010000000000010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010101000101000100000001010101000101010001010000010101010100000101000100000101000001000000000001000001010000010001010001010000"
                 },
-        /*  6*/ { BARCODE_AUSPOST, "23456789PQRSTUVWXY", 0, 3, 133, "62 Custom 3 C encoding GDSET 2nd part",
+        /*  8*/ { BARCODE_AUSPOST, "23456789PQRSTUVWXY", 0, 3, 133, "62 Custom 3 C encoding GDSET 2nd part",
                     "1000001010001000101010101000001000100000001010001010001010000000101000101000100000101000101000100000001000101000101010101000101010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010101010001000000010101010001010001000101000100000101010101010100010101010001010000010001010101000000010001000001010101000000"
                 },
-        /*  7*/ { BARCODE_AUSPOST, "34567890Zcefgijklm", 0, 3, 133, "62 Custom 3 C encoding GDSET 3rd part",
+        /*  9*/ { BARCODE_AUSPOST, "34567890Zcefgijklm", 0, 3, 133, "62 Custom 3 C encoding GDSET 3rd part",
                     "1000001010001010101010000010001000000010101000001010001010000010100010100010001010001010000010000000100000101000100000001010001010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010100010000000101010100010100010101010100010000010000000100000000000001000000000001000000010100000101000000010101010100010000"
                 },
-        /*  8*/ { BARCODE_AUSPOST, "12345678lnopqrstuv", 0, 3, 133, "62 Custom 3 C encoding GDSET 4th part",
+        /* 10*/ { BARCODE_AUSPOST, "12345678lnopqrstuv", 0, 3, 133, "62 Custom 3 C encoding GDSET 4th part",
                     "1000001010001010100010101010100000100010000010000000100000000000001000001000000000000000100000100000000000001010001010101000000010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010101000101000100000001010101000101000000010000010100010001010000010001010000000100000000000100000100000001010001000100000000"
                 },
-        /*  9*/ { BARCODE_AUSPOST, "09876543wxy# ", 0, 3, 103, "59 Custom 2 C encoding GDSET 5th part",
+        /* 11*/ { BARCODE_AUSPOST, "09876543wxy# ", 0, 3, 103, "59 Custom 2 C encoding GDSET 5th part",
                     "1000100000101010001000000010001010001010101000001000001000000010100010100000100010000000000010100010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000001000101010001010101000101000100000001000001000000000001010000010100000001010001000001000100000000"
                 },
-        /* 10*/ { BARCODE_AUSREPLY, "12345678", 0, 3, 73, "Verified manually against tec-it",
+        /* 12*/ { BARCODE_AUSREPLY, "12345678", 0, 3, 73, "Verified manually against tec-it",
                     "1000101010001010100010101010100000100010000000001000001000000000100010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000000000101000101000100000001010101000101000000000100010101000101000000"
                 },
-        /* 11*/ { BARCODE_AUSROUTE, "34567890", 0, 3, 73, "Verified manually against tec-it",
+        /* 13*/ { BARCODE_AUSROUTE, "34567890", 0, 3, 73, "Verified manually against tec-it",
                     "1000000000101010101010000010001000000010101000100010101010000000101000100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000101010000010000000101010100010100010101000100010101010001010001000000"
                 },
-        /* 12*/ { BARCODE_AUSREDIRECT, "98765432", 0, 3, 73, "Verified manually against tec-it",
+        /* 14*/ { BARCODE_AUSREDIRECT, "98765432", 0, 3, 73, "Verified manually against tec-it",
                     "1000001010000010000000100010100010101010100000101010101000100010100010100"
                     "1010101010101010101010101010101010101010101010101010101010101010101010101"
                     "0000001010100010101010001010001000000010101000000000001010101000001010000"
diff --git a/backend/tests/testcommon.c b/backend/tests/testcommon.c
index c207b539..153a1b3e 100644
--- a/backend/tests/testcommon.c
+++ b/backend/tests/testcommon.c
@@ -2695,8 +2695,7 @@ int testUtilBwipp(int index, const struct zint_symbol *symbol, int option_1, int
                         mode = 4;
                     } else {
                         for (i = 0; i < primary_len - 6; i++) {
-                            if (((symbol->primary[i] < '0') || (symbol->primary[i] > '9'))
-                                    && (symbol->primary[i] != ' ')) {
+                            if (!z_isdigit(symbol->primary[i]) && (symbol->primary[i] != ' ')) {
                                 mode = 3;
                                 break;
                             }
@@ -2821,7 +2820,7 @@ int testUtilBwipp(int index, const struct zint_symbol *symbol, int option_1, int
                     memcpy(macro_eci_buf, bwipp_data + 10, 13); /* Macro */
                     memcpy(bwipp_data + 13, bwipp_data, 10); /* ECI */
                     memcpy(bwipp_data, macro_eci_buf, 13);
-                } else if (data[4] >= '0' && data[4] <= '9' && data[5] >= '0' && data[5] <= '9') {
+                } else if (z_isdigit(data[4]) && z_isdigit(data[5])) {
                     memcpy(macro_eci_buf, bwipp_data, 10); /* ECI */
                     memcpy(bwipp_data, bwipp_data + 10, 9); /* Macro */
                     memcpy(bwipp_data + 9, macro_eci_buf, 10);
@@ -3119,7 +3118,7 @@ int testUtilBwippCmp(const struct zint_symbol *symbol, char *msg, char *cmp_buf,
     if (symbol->symbology == BARCODE_ULTRA) {
         static const char map[] = { '8', '1', '2', '3', '4', '5', '6', '7', '8', '7' };
         for (i = 0; i < cmp_len; i++) {
-            if (cmp_buf[i] >= '0' && cmp_buf[i] <= '9') {
+            if (z_isdigit(cmp_buf[i])) {
                 cmp_buf[i] = map[cmp_buf[i] - '0'];
             }
         }
diff --git a/backend/tools/gen_eci_mb_h.php b/backend/tools/gen_eci_mb_h.php
index 6f7ce247..e907de4e 100644
--- a/backend/tools/gen_eci_mb_h.php
+++ b/backend/tools/gen_eci_mb_h.php
@@ -6,7 +6,7 @@
 */
 /* SPDX-License-Identifier: BSD-3-Clause */
 /*
- * To create "backend/eci_mb.h" (from project root directory):
+ * To create "backend/eci_big5/gb18030/gb2312/gbk/ksx1001/sjis.h" (from project root directory):
  *
  *   php backend/tools/gen_eci_mb_h.php
  *
@@ -14,7 +14,7 @@
  *       https://haible.de/bruno/charsets/conversion-tables/GB18030.tar.bz2
  *       using the version jdk-1.4.2/GB18030.TXT
  */
-// 'zint.assertions' should set to 1 in php.ini
+// 'zend.assertions' should set to 1 in php.ini
 
 $copyright_text = <<<'EOD'
 
@@ -59,13 +59,12 @@ $year = 2022;
 function out_header(&$out, $name, $descr, $file, $start_year = 0, $extra_comment = '') {
     global $copyright_text, $basename, $year;
     $caps = strtoupper($name);
-    $out[] = '/*  ' . $name . '.h - tables for Unicode to ' . $descr . ',';
-    $out[] = '    ' . 'generated by "backend/tools/' . $basename . '" from';
+    $out[] = '/*  ' . $name . '.h - tables for Unicode to ' . $descr . ', generated by "backend/tools/' . $basename . '"';
     if ($extra_comment !== '') {
-        $out[] = '    "' . $file . '"';
+        $out[] = '    from "' . $file . '"';
         $out[] = '    ' . $extra_comment . ' */';
     } else {
-        $out[] = '    "' . $file . '" */';
+        $out[] = '    from "' . $file . '" */';
     }
     $out[] = '/*';
     $out[] = '    libzint - the open source barcode library';
diff --git a/backend/tools/gen_eci_sb_h.php b/backend/tools/gen_eci_sb_h.php
index 27039504..dbeec0f0 100644
--- a/backend/tools/gen_eci_sb_h.php
+++ b/backend/tools/gen_eci_sb_h.php
@@ -4,6 +4,7 @@
     libzint - the open source barcode library
     Copyright (C) 2022 Robin Stuart <rstuart114@gmail.com>
 */
+/* SPDX-License-Identifier: BSD-3-Clause */
 /*
  * To create "backend/eci_sb.h" (from project root directory):
  *
@@ -24,11 +25,11 @@ $out_dirname = isset($opts['o']) ? $opts['o'] : ($dirname . '/..'); // Where to
 $out = array();
 
 $head = <<<'EOD'
-/*  eci_sb.h - Extended Channel Interpretations single-byte,
-    generated by "backend/tools/gen_eci_sb_h.php" from
-    "https://unicode.org/Public/MAPPINGS/ISO8859/8859-*.TXT" and
-    "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP125*.TXT" */
-/* libzint - the open source barcode library
+/*  eci_sb.h - Extended Channel Interpretations single-byte, generated by "backend/tools/gen_eci_sb_h.php"
+    from "https://unicode.org/Public/MAPPINGS/ISO8859/8859-*.TXT"
+    and "https://unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP125*.TXT" */
+/*
+    libzint - the open source barcode library
     Copyright (C) 2021-2022 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
diff --git a/docs/images/gui_export.png b/docs/images/gui_export.png
index 32c6d2c6..c1159a98 100644
Binary files a/docs/images/gui_export.png and b/docs/images/gui_export.png differ
diff --git a/docs/images/gui_sequence.png b/docs/images/gui_sequence.png
index c056ac8f..ad03b4dc 100644
Binary files a/docs/images/gui_sequence.png and b/docs/images/gui_sequence.png differ
diff --git a/docs/manual.pmd b/docs/manual.pmd
index 7fef5f62..cb468fbe 100644
--- a/docs/manual.pmd
+++ b/docs/manual.pmd
@@ -470,7 +470,7 @@ Sequence    Equivalent
 `\uNNNN`                        Any 16-bit Unicode BMP[^2] character where
                                 NNNN is hexadecimal
 
-`\UNNNNNN`                      Any 20-bit Unicode character where NNNNNN
+`\UNNNNNN`                      Any 21-bit Unicode character where NNNNNN
                                 is hexadecimal (maximum 0x10FFFF)
 ---------------------------------------------------------------------------
 
diff --git a/docs/manual.txt b/docs/manual.txt
index ef5e7a2d..50de6a9a 100644
--- a/docs/manual.txt
+++ b/docs/manual.txt
@@ -620,7 +620,7 @@ sequences are shown in the table below.
   \uNNNN                           Any 16-bit Unicode BMP[2] character where
                                    NNNN is hexadecimal
 
-  \UNNNNNN                         Any 20-bit Unicode character where NNNNNN
+  \UNNNNNN                         Any 21-bit Unicode character where NNNNNN
                                    is hexadecimal (maximum 0x10FFFF)
   ----------------------------------------------------------------------------
 
@@ -4246,7 +4246,7 @@ OPTIONS
                                 hexadecimal
         \uNNNN   (U+NNNN)       Any 16-bit Unicode BMP character
                                 where NNNN is hexadecimal
-        \UNNNNNN (U+NNNNNN)     Any 20-bit Unicode character
+        \UNNNNNN (U+NNNNNN)     Any 21-bit Unicode character
                                 where NNNNNN is hexadecimal
 
 --fast
diff --git a/docs/zint.1 b/docs/zint.1
index 963eb483..f2d86f1a 100644
--- a/docs/zint.1
+++ b/docs/zint.1
@@ -186,7 +186,7 @@ The escape sequences are:
                         hexadecimal
 \[rs]uNNNN   (U+NNNN)       Any 16-bit Unicode BMP character
                         where NNNN is hexadecimal
-\[rs]UNNNNNN (U+NNNNNN)     Any 20-bit Unicode character
+\[rs]UNNNNNN (U+NNNNNN)     Any 21-bit Unicode character
                         where NNNNNN is hexadecimal
 \f[R]
 .fi
diff --git a/docs/zint.1.pmd b/docs/zint.1.pmd
index bfbac6f0..bc12a79c 100644
--- a/docs/zint.1.pmd
+++ b/docs/zint.1.pmd
@@ -139,7 +139,7 @@ Paintbrush (`PCX`), Portable Network Format (`PNG`), Scalable Vector Graphic (`S
                                 hexadecimal
         \uNNNN   (U+NNNN)       Any 16-bit Unicode BMP character
                                 where NNNN is hexadecimal
-        \UNNNNNN (U+NNNNNN)     Any 20-bit Unicode character
+        \UNNNNNN (U+NNNNNN)     Any 21-bit Unicode character
                                 where NNNNNN is hexadecimal
 
 `--fast`
diff --git a/frontend_qt/extSequence.ui b/frontend_qt/extSequence.ui
index a2679c65..d0e67795 100644
--- a/frontend_qt/extSequence.ui
+++ b/frontend_qt/extSequence.ui
@@ -133,7 +133,7 @@
             </property>
            </widget>
           </item>
-          <item row="3" column="1">
+          <item row="4" column="0" colspan="2">
            <widget class="QLineEdit" name="linSeqFormat">
             <property name="toolTip">
              <string>Format sequence using special characters&lt;table cellspacing=&quot;3&quot;&gt;
@@ -148,7 +148,7 @@
             </property>
            </widget>
           </item>
-          <item row="4" column="0" colspan="2">
+          <item row="5" column="0" colspan="2">
            <layout class="QHBoxLayout" name="horzLayoutSeqCreateBtn">
             <item>
              <spacer name="horzSpacerSeqCreateBtn">
diff --git a/frontend_qt/main.cpp b/frontend_qt/main.cpp
index a61f2e28..a7d395d8 100644
--- a/frontend_qt/main.cpp
+++ b/frontend_qt/main.cpp
@@ -28,6 +28,10 @@ int main(int argc, char *argv[])
     /* Suppresses "Qt WebEngine seems to be initialized from a plugin" warning */
     QApplication::setAttribute(Qt::AA_ShareOpenGLContexts);
 #endif
+#if defined(_WIN32) && QT_VERSION >= 0x50A01
+    /* Suppresses help question mark in dialogs */
+    QApplication::setAttribute(Qt::AA_DisableWindowContextHelpButton);
+#endif
 
     QApplication app(argc, argv);
 
diff --git a/frontend_qt/mainWindow.ui b/frontend_qt/mainWindow.ui
index a642e585..70367258 100644
--- a/frontend_qt/mainWindow.ui
+++ b/frontend_qt/mainWindow.ui
@@ -25,9 +25,6 @@
    <locale language="English" country="UnitedStates"/>
   </property>
   <layout class="QVBoxLayout" name="vLayoutMain">
-   <property name="sizeConstraint">
-    <enum>QLayout::SetMinimumSize</enum>
-   </property>
    <item>
     <widget class="QGraphicsView" name="view">
      <property name="minimumSize">
@@ -1535,7 +1532,7 @@ or import from file</string>
 &lt;tr&gt;&lt;td&gt;\dNNN&amp;nbsp;&lt;/td&gt;&lt;td&gt;8-bit character (N decimal)&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;\xNN&amp;nbsp;&lt;/td&gt;&lt;td&gt;8-bit character (N hex)&lt;/td&gt;&lt;/tr&gt;
 &lt;tr&gt;&lt;td&gt;\uNNNN&amp;nbsp;&lt;/td&gt;&lt;td&gt;16-bit Unicode BMP (N hex)&lt;/td&gt;&lt;/tr&gt;
-&lt;tr&gt;&lt;td&gt;\UNNNNNN&amp;nbsp;&lt;/td&gt;&lt;td&gt;20-bit Unicode (N hex)&lt;/td&gt;&lt;/tr&gt;
+&lt;tr&gt;&lt;td&gt;\UNNNNNN&amp;nbsp;&lt;/td&gt;&lt;td&gt;21-bit Unicode (N hex)&lt;/td&gt;&lt;/tr&gt;
 &lt;/table&gt;</string>
                </property>
                <property name="text">