Can vim syntax regions be made to touch/overlap?

Question

So a while ago I had decided to learn more about how vim's syntax files work, by creating my own. My goal was to create a simple syntax file that would split the file into 3 parts based on delimiters, and include pre-existing syntax files for two of those three parts.

This is an example file:

Some text, unstyled

==================== Log
(Output of git log)

==================== Diff
(Output of diff)

The goal was to apply git.vim to just the log, and diff.vim to just the diff, excluding the two headers.¹ This is what my syntax file ended up looking like:

if exists("b:current_syntax")
    finish
endif

syntax include @gitlog $VIMRUNTIME/syntax/git.vim
syntax region GitLog
    \ start=/^===* Log/
    \ end=/^===* Diff/
    \ contains=@gitlog

syntax include @gitdiff $VIMRUNTIME/syntax/diff.vim
syntax region Diff
    \ start=/^===* Diff/
    \ end=/\n\n/
    \ contains=@gitdiff

let b:current_syntax = "logdiff"

Note how end on the first region is the same as start on the second region. This doesn't work; the second region is apparently not detected and syntax highlighting is not applied.

I can make it work by loosening the regex to end=/^===/ and start=/=== Diff/, so that the regions don't touch, but don't particularly like that - it's less obvious that one is supposed to start where the other ends.

Is there a way to allow two region definitions to touch the same characters (and/or make the matching edges exclusive instead of inclusive) or am I stuck with the looser regex?

_{¹(Yes, I know git.vim includes diff.vim, but this was a learning exercise)}

Answer 1

You can tell Vim regex engine where to start next match.

So far I know there are 2 ways:

1. Use \ze to set the end of a match:

   syntax region GitLog
       \ start=/^===* Log/
       \ end=/\ze^===* Diff/
       \ contains=@gitlog
   

2. Use positive lookahead, \@=, which is called zero-width matching in Vim:

   syntax region GitLog
       \ start=/^===* Log/
       \ end=/\(^===* Diff\)\@=/
       \ contains=@gitlog
   

So the end-of-match "pointer" kind of rewinds to the beginning of ^===* Diff line, such that region Diff's start will start its matching at ^===* Diff line again.