How to stop Vim markdown syntax from highlighting as italic asterisks used to denote bold?

Question

Using Vim 7.4 on Windows in ConEmu (though I have seen the same thing on other platforms/setups), I notice that the syntax highlighting is matching the beginning and ending double-asterisks as italic sub-regions within the bold region that they denote. This is an eyesore:

After digging around, I think I have found the source of this problem (from $VIMRUNTIME/syntax/markdown.vim):

syn region markdownItalic start="\S\@<=\*\|\*\S\@=" end="\S\@<=\*\|\*\S\@=" keepend contains=markdownLineStart
syn region markdownItalic start="\S\@<=_\|_\S\@=" end="\S\@<=_\|_\S\@=" keepend contains=markdownLineStart
syn region markdownBold start="\S\@<=\*\*\|\*\*\S\@=" end="\S\@<=\*\*\|\*\*\S\@=" keepend contains=markdownLineStart,markdownItalic
syn region markdownBold start="\S\@<=__\|__\S\@=" end="\S\@<=__\|__\S\@=" keepend contains=markdownLineStart,markdownItalic
syn region markdownBoldItalic start="\S\@<=\*\*\*\|\*\*\*\S\@=" end="\S\@<=\*\*\*\|\*\*\*\S\@=" keepend contains=markdownLineStart
syn region markdownBoldItalic start="\S\@<=___\|___\S\@=" end="\S\@<=___\|___\S\@=" keepend contains=markdownLineStart

And farther down:

hi def link markdownItalic                htmlItalic
hi def link markdownBold                  htmlBold
hi def link markdownBoldItalic            htmlBoldItalic

As you can see, the bold accepts italics as a subregion. The problem is if I remove markdownItalic from the contains=, this:

no longer works right:

even though it fixed the other problem. I also trying substituting \S in the regexes for italic to be [^*] but that didn't work either. Also, installing Plastic Boy's Markdown plugin didn't fix it.

Any ideas on how to get around this annoying case?

Answer 1

So this basic concept does work:

I also trying substituting \S in the regexes for italic to be [^*] but that didn't work either.

Just copy $VIMRUNTIME/syntax/markdown.vim into ~/.vim/syntax/ and change the two syn region markdownItalic... lines to be

syn region markdownItalic start="[^* ]\@<=\*\*\@!\|\*\@<!\*[^* ]\@=" end="[^* ]\@<=\*\|\*\@<!\*[^* ]\@=" keepend contains=markdownLineStart
syn region markdownItalic start="[^_ ]\@<=__\@!\|_\@<!_[^_]\@=" end="[^_ ]\@<=_\|_\@<!_[^_]\@=" keepend contains=markdownLineStart

Also, notably, it seems Tim Pope's current vim-markdown does not have the problem (though as of this writing it has others related to italics; it seems this is a difficult problem to solve with Vim syntax highlighting).