DATAMATRIX: add new options DM_B256_START and DM_C40_START to

`options_3`, allowing forcing of Base 256 or C40 mode a la BWIPP
  for initial no. of characters specified in `option_1`, with 0
  meaning all (CLI "--dmb256=" and "--dmc40=", GUI also (apart
  from MAILMARK_2D, which may be added later);
  export masks `DM_B256_C40_START_MASK` & `DM_SQUARE_DMRE_MASK` in
  "zint.h"
ZBarcode_Encode_File: report filename (possibly truncated) in error
  message on failed open
GUI: uniquify some accelerators and add some child widget getter
  helpers to "mainwindow.cpp"
backend/DEVELOPER -> backend/README, with some expansion
debian/copyright: a few more fixes
BWIPP/pandoc: update to latest
tests/fuzz: adjust for new DATAMATRIX options

docs/manual.html

@@ -6504,6 +6504,12 @@ ISO/IEC standard placement, use option <code>--dmiso144</code> (API
 <code>option_3 |= DM_ISO_144</code>).</p>
 <p>For a faster but less optimal encodation, the <code>--fast</code>
 option (API <code>input_mode |= FAST_MODE</code>) may be used.</p>
+<p>The encodation mode of initial input characters may be forced using
+the <code>--dmb256</code> (API <code>option_3 |= DM_B256_START</code>)
+and <code>--dmc40</code> (API <code>option_3 |= DM_C40_START</code>)
+options. Both take an integer (API <code>option_1</code>) which
+specifies how many initial characters to encode in the respective mode,
+with <code>0</code> meaning all.</p>
 <p>Data Matrix supports Structured Append of up to 16 symbols and a
 numeric ID (file identifications), which can be set by using the
 <code>--structapp</code> option (see <a href="#structured-append">4.17
@@ -9249,6 +9255,16 @@ anything.</p>
 pipe or a file. Use <code>--filetype</code> to specify output
 format.</p>
 </dd>
+<dt><code>--dmb256=INTEGER</code></dt>
+<dd>
+<p>For Data Matrix symbols, encode the first <em>INTEGER</em> input
+characters in Base 256 mode. 0 means all input.</p>
+</dd>
+<dt><code>--dmc40=INTEGER</code></dt>
+<dd>
+<p>For Data Matrix symbols, encode the first <em>INTEGER</em> input
+characters in C40 mode. 0 means all input.</p>
+</dd>
 <dt><code>--dmiso144</code></dt>
 <dd>
 <p>For Data Matrix symbols, use the standard ISO/IEC codeword placement

docs/manual.pmd

@@ -4345,6 +4345,12 @@ placement, use option `--dmiso144` (API `option_3 |= DM_ISO_144`).
 For a faster but less optimal encodation, the `--fast` option (API `input_mode
 |= FAST_MODE`) may be used.
 
+The encodation mode of initial input characters may be forced using the
+`--dmb256` (API `option_3 |= DM_B256_START`) and `--dmc40` (API `option_3 |=
+DM_C40_START`) options. Both take an integer (API `option_1`) which specifies
+how many initial characters to encode in the respective mode, with `0` meaning
+all.
+
 Data Matrix supports Structured Append of up to 16 symbols and a numeric ID
 (file identifications), which can be set by using the `--structapp` option (see
 [4.17 Structured Append]) (API `structapp`). The ID consists of 2 numbers `ID1`

docs/manual.txt

@@ -4143,6 +4143,11 @@ placement, use option --dmiso144 (API option_3 |= DM_ISO_144).
 For a faster but less optimal encodation, the --fast option (API
 input_mode |= FAST_MODE) may be used.
 
+The encodation mode of initial input characters may be forced using the --dmb256
+(API option_3 |= DM_B256_START) and --dmc40 (API option_3 |= DM_C40_START)
+options. Both take an integer (API option_1) which specifies how many initial
+characters to encode in the respective mode, with 0 meaning all.
+
 Data Matrix supports Structured Append of up to 16 symbols and a numeric ID
 (file identifications), which can be set by using the --structapp option (see
 4.17 Structured Append) (API structapp). The ID consists of 2 numbers ID1 and
@@ -5321,6 +5326,16 @@ OPTIONS
     Send output to stdout, which in most cases should be re-directed to a pipe
     or a file. Use --filetype to specify output format.
 
+--dmb256=INTEGER
+
+    For Data Matrix symbols, encode the first INTEGER input characters in Base
+    256 mode. 0 means all input.
+
+--dmc40=INTEGER
+
+    For Data Matrix symbols, encode the first INTEGER input characters in C40
+    mode. 0 means all input.
+
 --dmiso144
 
     For Data Matrix symbols, use the standard ISO/IEC codeword placement for 144

docs/zint.1

@@ -1,4 +1,4 @@
-.\" Automatically generated by Pandoc 3.9
+.\" Automatically generated by Pandoc 3.9.0.2
 .\"
 .TH "ZINT" "1" "March 2026" "Version 2.16.0.9"
 .SH NAME
@@ -124,6 +124,16 @@ Send output to stdout, which in most cases should be re\-directed to a
 pipe or a file.
 Use \f[CR]\-\-filetype\f[R] to specify output format.
 .TP
+\f[CR]\-\-dmb256=INTEGER\f[R]
+For Data Matrix symbols, encode the first \f[I]INTEGER\f[R] input
+characters in Base 256 mode.
+0 means all input.
+.TP
+\f[CR]\-\-dmc40=INTEGER\f[R]
+For Data Matrix symbols, encode the first \f[I]INTEGER\f[R] input
+characters in C40 mode.
+0 means all input.
+.TP
 \f[CR]\-\-dmiso144\f[R]
 For Data Matrix symbols, use the standard ISO/IEC codeword placement for
 144 x 144 (\f[CR]\-\-vers=24\f[R]) sized symbols, instead of the default

docs/zint.1.pmd

@@ -113,6 +113,14 @@ Paintbrush (`PCX`), Portable Network Format (`PNG`), Scalable Vector Graphic (`S
 :   Send output to stdout, which in most cases should be re-directed to a pipe or a file. Use `--filetype` to specify
     output format.
 
+`--dmb256=INTEGER`
+
+:   For Data Matrix symbols, encode the first *INTEGER* input characters in Base 256 mode. 0 means all input.
+
+`--dmc40=INTEGER`
+
+:   For Data Matrix symbols, encode the first *INTEGER* input characters in C40 mode. 0 means all input.
+
 `--dmiso144`
 
 :   For Data Matrix symbols, use the standard ISO/IEC codeword placement for 144 x 144 (`--vers=24`) sized symbols,