Vim has had syntax high­light­ing since version 5.0 in 1998. It quickly became in­dis­pens­able. It’s hard to go back to looking at mono­chro­mat­ic source code after you’ve become accustomed to syntax high­light­ing.

The syntax high­light­ing is tied into Vim’s support for col­orschemes, which define colors for the fun­da­men­tal syntax groups like Number, Comment, and String. The syntax high­light­ing for a particular language defines custom syntax groups for specific language features, such as cppEx­cep­tions or htmlEndTag,

The custom syntax groups are linked to the underlying fun­da­men­tal syntax groups. Hence, if you change your col­orscheme, your syntax high­light­ing is updated au­to­mat­i­cal­ly.

The re­Struc­tured­Text syntax high­light­ing in Vim 7.2 has some short­com­ings, in my opinion. For example, *italic* shows up as italic in gVim, but in the same color as regular text, while **bold** shows up in a different color, but not bolded.

When you declare a syntax group, you can either link it to another gropu and pick up that’s one color and fontstyle, or you can give it a concrete fontstyle and color. If you do that, then the syntax group won’t change color when you change the col­orscheme.

After much poking around, I found a way to set a syntax group’s fontstyle and link it to another group’s color: see hi def rstItalic and hi def rstBold below.

I also make use of certain Unicode characters in my re­Struc­tured­Text source, such as endash and emdash, which are very hard to tell apart in a fixed-width font—even though an emdash (—) is twice as wide as an endash (–) in a pro­por­tion­al font. Worse, a non-breaking space is invisible and can’t easily be dis­tin­guished from a normal space.

I provided custom high­light­ing for these Unicode characters and the various ‘curly’ “quotes”.

All of this goes into ~/.vim/syntax/rst.vim, which treats $VIMRUNTIME/syntax/rst.vim as a subroutine. I tried putting it into ~/.vim/after/syntax/rst.vim, which gets executed after $VIMRUNTIME/syntax/rst.vim completes, but then I can’t provide non-over­ride­able de­f­i­n­i­tions for rstEm­pha­sis and rst­StrongEm­pha­sis.

function! s:SynFgColor(hlgrp)
    return synIDattr(synIDtrans(hlID(a:hlgrp)), 'fg')
endfun

function! s:SynBgColor(hlgrp)
    return synIDattr(synIDtrans(hlID(a:hlgrp)), 'bg')
endfun

syn match rstEnumeratedList /^\s*[0-9#]\{1,3}\.\s/
syn match rstBulletedList /^\s*[+*-]\s/
syn match rstNbsp /[\xA0]/
syn match rstEmDash /[\u2014]/
syn match rstUnicode /[\u2013\u2018\u2019\u201C\u201D]/ " – ‘ ’ “ ”

exec 'hi def rstBold    term=bold cterm=bold gui=bold guifg=' . s:SynFgColor('PreProc')
exec 'hi def rstItalic  term=italic cterm=italic gui=italic guifg=' . s:SynFgColor('Statement')
exec 'hi def rstNbsp    gui=underline guibg=' . s:SynBgColor('ErrorMsg')
exec 'hi def rstEmDash  gui=bold guifg=' . s:SynFgColor('Title') . ' guibg='. s:SynBgColor('Folded')
exec 'hi def rstUnicode guifg=' . s:SynFgColor('Number')

hi link rstEmphasis       rstItalic
hi link rstStrongEmphasis rstBold
hi link rstEnumeratedList Operator
hi link rstBulletedList   Operator

source $VIMRUNTIME/syntax/rst.vim

syn cluster rstCruft                contains=rstEmphasis,rstStrongEmphasis,
      \ rstInterpretedText,rstInlineLiteral,rstSubstitutionReference,
      \ rstInlineInternalTargets,rstFootnoteReference,rstHyperlinkReference,
      \ rstNbsp,rstEmDash,rstUnicode