highlight sub-match in vim

Question

I'm trying to figure out how to highlight a specific portion of a match in vim.

Given the following example rule (taken from the coffeescript syntax file source):

syn match coffeeExtendedOp /\%(\S\s*\)\@<=[+\-*/%&|\^=!<>?.]\+\|[-=]>\|--\|++\|:/ display

This regular expression matches various coffeescript operators. The operators are highlighted (in my vimrc) like this:

hi Operator guifg=#ff0000

For example, since coffeeExtendedOp is linked to coffeeOperator which is linked to Operator, in the above source file. This all works, but I'm wondering how to specifically highlight the ++ operator matched in the above syn match with a different color, say blue, within my vimrc (that is, without altering the original source file above). I'm simply wondering if this is possible.

EDIT: I think the rules are placed under a cluster, so perhaps that's why it's not affecting anything. Is there a way to access the rule within the cluster?

EDIT: Question was clarified.

Solution:

syn match plusplus /++/ contained containedin=coffeeExtendedOp display
hi plusplus guifg=#0000ff

The problem now is that this only works when I run them as commands in vim, but not when I put it in my vimrc file. Any ideas? Could it be that the stuff is hidden behind the cluster? But then why is it visible in vim through a command? I tried including the syntax file but it didn't seem to have any effect.

Answer 1

Looking at the coffee.vim you linked to it seems like the dot belongs to the coffeeDotAccess syntax item. So you can highlight it just by doing this:

:hi coffeeDotAccess ctermfg=blue

Answer 2

I'm going to guess a bit at what you need. (I don't speak Coffeescript and your sample regex is way too complicated for me to start reading at the moment).

Transparent syntax items

You could have a look at transparent syntax rules: (http://vimdoc.sourceforge.net/htmldoc/usr_44.html)

In a C language file you would like to highlight the () text after a "while"
differently from the () text after a "for".  In both of these there can be
nested () items, which should be highlighted in the same way.  You must make
sure the () highlighting stops at the matching ).  This is one way to do this:

    :syntax region cWhile matchgroup=cWhile start=/while\s*(/ end=/)/
        \ contains=cCondNest
    :syntax region cFor matchgroup=cFor start=/for\s*(/ end=/)/
        \ contains=cCondNest
    :syntax region cCondNest start=/(/ end=/)/ contained transparent

Partial matches in regex

If you really just meant highlighting submatches, have a look at the the

\zs      start match
\ze      end match

In short,

:match Error /foo\zsbar\zered/

would highlight only 'bar' in 'foobarred'