bug: prevent "' from being a valid region (which is not)

Author: vhoyer

syntax/vue.vim

@@ -79,8 +79,16 @@ syn match   htmlArg "[@#v:a-z][-:.0-9_a-z]*\>" contained
 syn match htmlString /\(\([@#:]\|v-\)[-:.0-9_a-z]*=\)\@<=["']\{2\}/ containedin=ALLBUT,htmlComment
 
 " Actually provide the JavaScript syntax highlighting.
-syn region vueJavascriptInTemplate start=/\(\([@#:]\|v-\)[-:.0-9_a-z]*=\)\@<=["']/ms=e+1 keepend end=/["']/me=s-1 contains=@jsAll containedin=ALL
+
+" for mustaches quotes (`{{` and `}}`)
 syn region vueJavascriptInTemplate matchgroup=htmlSpecialChar start=/{{/ keepend end=/}}/ contains=@jsAll containedin=ALLBUT,htmlComment
+" for double quotes (")
+syn region vueJavascriptInTemplate start=/\(\([@#:]\|v-\)[-:.0-9_a-z]*=\)\@<="/ms=e+1 keepend end=/"/me=s-1 contains=@jsAll containedin=ALL
+" for single quotes (')
+syn region vueJavascriptInTemplate start=/\(\([@#:]\|v-\)[-:.0-9_a-z]*=\)\@<='/ms=e+1 keepend end=/'/me=s-1 contains=@jsAll containedin=ALL
+" It's necessary to have both because we can't start a region with double
+" quotes and it with a single quote, and removing `keepend` would result in
+" side effects.
 
 syntax sync fromstart