runtime(help): Update syntax, match tables at :help :digraph-table

Match the digraph tables to avoid false positive matches for helpSpecial
etc.  No syntax groups should match in these tables.

closes: #18738

Signed-off-by: Doug Kearns <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: dkearns

runtime/syntax/help.vim

@@ -1,7 +1,7 @@
 " Vim syntax file
 " Language:		Vim help file
 " Maintainer:		Doug Kearns <[email protected]>
-" Last Change:		2025 Oct 19
+" Last Change:		2025 Nov 13
 " Former Maintainer:	Bram Moolenaar <[email protected]>
 
 " Quit when a (custom) syntax file was already loaded
@@ -62,20 +62,6 @@ if has_key(g:help_example_languages, "vim9")
   syn cluster helpExampleHighlight_vim9 add=vim9LegacyHeader_HelpExample
 endif
 
-" builtin.txt
-syn region helpReturnType
-      \ start="^\t\tReturn type: "
-      \ end="^$"
-      \ contains=@vimType,helpHyperTextJump,helpSpecial
-      \ transparent
-syn match helpSpecial		contained "{type}" containedin=vimCompoundType
-
-" various.txt
-syn region helpExCommand_Version
-      \ start="^:ve\[rsion]\t\t"
-      \ end="\n\ze\n:ve\[rsion] {nr}"
-      \ contains=helpHyperTextEntry,helpHyperTextJump,helpOption
-
 if has("ebcdic")
   syn match helpHyperTextJump	"\\\@<!|[^"*|]\+|" contains=helpBar
   syn match helpHyperTextEntry	"\*[^"*|]\+\*\s"he=e-1 contains=helpStar
@@ -229,6 +215,26 @@ syn match helpDiffAdded		"\t[* ]Added\t\+[a-z].*"
 syn match helpDiffChanged	"\t[* ]Changed\t\+[a-z].*"
 syn match helpDiffRemoved	"\t[* ]Removed\t\+[a-z].*"
 
+" builtin.txt
+syn region helpReturnType
+      \ start="^\t\tReturn type: "
+      \ end="^$"
+      \ contains=@vimType,helpHyperTextJump,helpSpecial
+      \ transparent
+syn match helpSpecial		contained "{type}" containedin=vimCompoundType
+
+" digraph.txt
+syn region helpDigraphTable
+      \ start="*digraph-table\%(-mbyte\)\=\*"
+      \ end="^$"
+      \ contains=helpHyperTextEntry,helpHeader
+
+" various.txt
+syn region helpExCommand_Version
+      \ start="^:ve\[rsion]\t\t"
+      \ end="\n\ze\n:ve\[rsion] {nr}"
+      \ contains=helpHyperTextEntry,helpHyperTextJump,helpOption
+
 " Additionally load a language-specific syntax file "help_ab.vim".
 let s:i = match(expand("%"), '\.\a\ax$')
 if s:i > 0
@@ -238,7 +244,6 @@ unlet s:i
 
 syn sync minlines=40
 
-
 " Define the default highlighting.
 " Only used when an item doesn't have highlighting yet
 hi def link helpIgnore		Ignore

runtime/syntax/testdir/dumps/help_digraph_table_00.dump

@@ -0,0 +1,20 @@
+> +0&#ffffff0@74
+@56|*+0#ffffff16&|d+0#e000002&|i|g|r|a|p|h|-|t|a|b|l|e|*+0#ffffff16&| +0#0000000&@3
+|c+0#e000e06&|h|a|r| @1|d|i|g|r|a|p|h| @2|h|e|x| @4|d|e|c| @4|o|f@1|i|c|i|a|l| |n|a|m|e| +0#ffffff16&|~| +0#0000000&@27
+|^|@| @5|N|U| @5|0|x|0@1| @5|0| @4|N|U|L@1| |(|N|U|L|)| @32
+|^|A| @5|S|H| @5|0|x|0|1| @5|1| @4|S|T|A|R|T| |O|F| |H|E|A|D|I|N|G| |(|S|O|H|)| @20
+|^|B| @5|S|X| @5|0|x|0|2| @5|2| @4|S|T|A|R|T| |O|F| |T|E|X|T| |(|S|T|X|)| @23
+|^|C| @5|E|X| @5|0|x|0|3| @5|3| @4|E|N|D| |O|F| |T|E|X|T| |(|E|T|X|)| @25
+|^|D| @5|E|T| @5|0|x|0|4| @5|4| @4|E|N|D| |O|F| |T|R|A|N|S|M|I|S@1|I|O|N| |(|E|O|T|)| @17
+|^|E| @5|E|Q| @5|0|x|0|5| @5|5| @4|E|N|Q|U|I|R|Y| |(|E|N|Q|)| @29
+|^|F| @5|A|K| @5|0|x|0|6| @5|6| @4|A|C|K|N|O|W|L|E|D|G|E| |(|A|C|K|)| @25
+|^|G| @5|B|L| @5|0|x|0|7| @5|7| @4|B|E|L@1| |(|B|E|L|)| @32
+|^|H| @5|B|S| @5|0|x|0|8| @5|8| @4|B|A|C|K|S|P|A|C|E| |(|B|S|)| @28
+|^|I| @5|H|T| @5|0|x|0|9| @5|9| @4|C|H|A|R|A|C|T|E|R| |T|A|B|U|L|A|T|I|O|N| |(|H|T|)| @17
+|Ñ| @6|N|?| @5|0|x|d|1| @3|2|0|9| @4|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |N| |W|I|T|H| |T|I|L|D|E| @9
+@75
+|I|f| |y|o|u| |a|r|e| |u|s|i|n|g| |a| ||+0#ffffff16&|m+0#00e0e07&|u|l|t|i|b|y|t|e||+0#ffffff16&| +0#0000000&|'+0#00e0003&|e|n|c|o|d|i|n|g|'|,+0#0000000&| |V|i|m| |p|r|o|v|i|d|e|s| |t|h|i|s| |e|n|h|a|n|c|e|d| |s|e|t| |o
+|f| @73
+|a|d@1|i|t|i|o|n|a|l| |d|i|g|r|a|p|h|s|:| @54
+@75
+@57|1|,|0|-|1| @8|T|o|p| 

runtime/syntax/testdir/dumps/help_digraph_table_01.dump

@@ -0,0 +1,20 @@
+|Ñ+0&#ffffff0| @6|N|?| @5|0|x|d|1| @3|2|0|9| @4|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |N| |W|I|T|H| |T|I|L|D|E| @9
+@75
+|I|f| |y|o|u| |a|r|e| |u|s|i|n|g| |a| ||+0#ffffff16&|m+0#00e0e07&|u|l|t|i|b|y|t|e||+0#ffffff16&| +0#0000000&|'+0#00e0003&|e|n|c|o|d|i|n|g|'|,+0#0000000&| |V|i|m| |p|r|o|v|i|d|e|s| |t|h|i|s| |e|n|h|a|n|c|e|d| |s|e|t| |o
+|f| @73
+|a|d@1|i|t|i|o|n|a|l| |d|i|g|r|a|p|h|s|:| @54
+> @74
+@56|*+0#ffffff16&|d+0#e000002&|i|g|r|a|p|h|-|t|a|b|l|e|-|m|b|y|t
+|e|*+0#ffffff16&| +0#0000000&@72
+|c|h|a|r| @1|d|i|g|r|a|p|h| @2|h|e|x| @4|d|e|c| @4|o|f@1|i|c|i|a|l| |n|a|m|e| @29
+|Ā| @6|A|-| @5|0|1|0@1| @3|0|2|5|6| @3|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |A| |W|I|T|H| |M|A|C|R|O|N| @8
+|ā| @6|a|-| @5|0|1|0|1| @3|0|2|5|7| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |A| |W|I|T|H| |M|A|C|R|O|N| @10
+|Ă| @6|A|(| @5|0|1|0|2| @3|0|2|5|8| @3|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |A| |W|I|T|H| |B|R|E|V|E| @9
+|ă| @6|a|(| @5|0|1|0|3| @3|0|2|5|9| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |A| |W|I|T|H| |B|R|E|V|E| @11
+|Ą| @6|A|;| @5|0|1|0|4| @3|0|2|6|0| @3|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |A| |W|I|T|H| |O|G|O|N|E|K| @8
+|ą| @6|a|;| @5|0|1|0|5| @3|0|2|6|1| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |A| |W|I|T|H| |O|G|O|N|E|K| @10
+|Ć| @6|C|'| @5|0|1|0|6| @3|0|2|6|2| @3|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |C| |W|I|T|H| |A|C|U|T|E| @9
+|ć| @6|c|'| @5|0|1|0|7| @3|0|2|6|3| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |C| |W|I|T|H| |A|C|U|T|E| @11
+|Ĉ| @6|C|>| @5|0|1|0|8| @3|0|2|6|4| @3|L|A|T|I|N| |C|A|P|I|T|A|L| |L|E|T@1|E|R| |C| |W|I|T|H| |C|I|R|C|U|M|F|L|E|X| @4
+|ĉ| @6|c|>| @5|0|1|0|9| @3|0|2|6|5| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |C| |W|I|T|H| |C|I|R|C|U|M|F|L|E|X| @6
+@57|1|8|,|0|-|1| @7|8|6|%| 

runtime/syntax/testdir/dumps/help_digraph_table_02.dump

@@ -0,0 +1,20 @@
+|ĉ+0&#ffffff0| @6|c|>| @5|0|1|0|9| @3|0|2|6|5| @3|L|A|T|I|N| |S|M|A|L@1| |L|E|T@1|E|R| |C| |W|I|T|H| |C|I|R|C|U|M|F|L|E|X| @6
+@75
+@1>v|i|m|:|t|w|=|7|8|:|t|s|=|8|:|n|o|e|t|:|f|t|=|h|e|l|p|:|n|o|r|l|:| @40
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+| +0#0000000&@56|3|2|,|2| @9|B|o|t|