How can I override a syntax keyword match?

Question

I would like the html tag attribute id to be highlighted differently from the rest of the tag attributes.

Like the Atom editor:

Given this line from the html5.vim plugin

syn keyword htmlArg contained id

I have tried this:

syn match htmlArgId /id/ containedin=ALL
hi htmlArgId guifg=blue

but it doesn't work it only highlights id outside of html tags.

Answer 1

Well you can of course dive into the complex syntax rules, see @Carpetsmoker's answer. However that might not always work correctly, depending on the order of the syntax rules and their priorities. Therefore, for such simple things it is usually better to use matchadd() function for highlighting special items in addition to the syntax rule.

First define your highlighting group you want to use:

hi htmlTagID ctermbg=blue guifg=blue
call matchadd('htmlTagID', '\<id\>\ze=')

This could be put into a filetype plugin, like ~/.vim/after/ftplugin/html.vim (create non-existing directories). For a more complete solution, you would need to store the return value of matchadd, to be able to clear the match later with matchdelete().

Note, matching is window-local so if you have the same buffer open in several windows, you might not see the highlighting in every window. For that you would also need to call the highlighting function on a WinEnter autocommand (or similar).

Answer 2

You'll need to modify the contains of syn region htmlTag to include your new htmlArgId. The full line would be:

syn region htmlTag start=+<[^/]+ end=+>+ fold contains=htmlTagN,htmlString,htmlArg,htmlValue,htmlTagError,htmlEvent,htmlCssDefinition,@htmlPreproc,@htmlArgCluster,htmlArgId

I just tacked on ,htmlArgId at the end; the rest is from /usr/share/vim/vim80/syntax/html.vim.

After that you can just use:

syn keyword htmlArgId contained id
hi htmlArgId ctermfg=blue guifg=blue

You can add this in your vimrc with an autocmd (autocmd Syntax html ...), or you can put it in ~/.vim/after/syntax/html.vim. See How can I add additional syntax highlighting rules in my local vimrc? for details on that.