HTML: fix broken CSS syntax within HTML attributes, add legacy HTML3 color attribute support

Author: adamhotep

after/syntax/html.vim

@@ -1,2 +1,35 @@
 " default html syntax should already be including the css syntax
-call css_color#init('none', 'none', 'htmlString,htmlCommentPart')
+" but tag style attributes don't properly apply CSS syntax (as of vim 9.0.1378).
+" Correct the bug by replacing htmlCssDefinition with a new htmlCssContent: {{{
+syn keyword htmlCssArg		contained containedin=htmlTag nextgroup=htmlCssEq style
+syn match htmlCssEq		contained +=+ nextgroup=htmlCssQuote
+syn match htmlCssQuote		contained +["']+ nextgroup=htmlCssContent
+syn region htmlCssContent	contained start=+\%("\)\@<=.+ end=+"+ keepend contains=cssTagName,cssAttributeSelector,cssClassName,cssIdentifier,cssAtRule,cssAttrRegion,css.*Prop,cssComment,cssValue.*,cssColor,cssURL,cssImportant,cssCustomProp,cssError,cssStringQ,cssFunction,cssUnicodeEscape,cssVendor,cssHacks,cssNoise
+syn region htmlCssContent	contained start=+\%('\)\@<=.+ end=+'+ keepend contains=cssTagName,cssAttributeSelector,cssClassName,cssIdentifier,cssAtRule,cssAttrRegion,css.*Prop,cssComment,cssValue.*,cssColor,cssURL,cssImportant,cssCustomProp,cssError,cssStringQ,cssFunction,cssUnicodeEscape,cssVendor,cssHacks,cssNoise
+
+hi def link htmlCssArg		htmlArg
+hi def link htmlCssEq		htmlTag
+hi def link htmlCssQuote	htmlString
+" end bugfix }}}
+
+" Legacy HTML 3-style color declarations (depcecated) {{{
+" Search https://www.w3.org/TR/html4/index/attributes.html for `%Color;`
+" Technically, these must be named or #RRGGBB, but both FF and Chrome simply
+" map it to CSS, supporting #RGB, #RGBA, and #RRGGBBAA (though alpha is ignored)
+syn region  htmlTag		start=+<\s*body\s+   end=+>+ fold contains=htmlTagN,htmlString,htmlArg,htmlValue,htmlTagError,htmlEvent,htmlCssDefinition,@htmlPreproc,@htmlArgCluster,htmlTagBodyColors
+syn keyword htmlTagBodyColors	contained nextgroup=htmlLegacyColor text bgcolor link alink vlink
+syn region  htmlTag		start=+<\s*\%(table\|t[rdh]\)\s+   end=+>+ fold contains=htmlTagN,htmlString,htmlArg,htmlValue,htmlTagError,htmlEvent,htmlCssDefinition,@htmlPreproc,@htmlArgCluster,htmlBgColors
+syn keyword htmlBgColors	contained nextgroup=htmlLegacyColor bgcolor
+syn region  htmlTag		start=+<\s*\%(base\)\?font\s+   end=+>+ fold contains=htmlTagN,htmlString,htmlArg,htmlValue,htmlTagError,htmlEvent,htmlCssDefinition,@htmlPreproc,@htmlArgCluster,htmlFgColors
+syn keyword htmlFgColors	contained nextgroup=htmlLegacyColor color
+syn region htmlLegacyColor	contained start=+="+ end=+"+ contains=cssColor
+syn region htmlLegacyColor	contained start=+='+ end=+'+ contains=cssColor
+
+hi def link htmlTagBody		htmlTagName
+hi def link htmlTagBodyColors	htmlArg
+hi def link htmlBgColors	htmlArg
+hi def link htmlFgColors	htmlArg
+" end legacy HTML-3 color attributes }}}
+
+" apply colors within HTML style attributes, legacy HTML-3 attributes, and comments
+call css_color#init('none', 'none', 'htmlCssContent,htmlLegacyColor,htmlCommentPart')