Vim custom syntax highlighting: highlight "word=value" without spaces in between

Question

I've asked this question on StackOverflow and they suggested to ask it here. I am trying to set a custom syntax highlighting for BSD rc.conf file which looks like:

name=YES
anothername=NO
third="options"

I created years agoo a syntax file:

if version < 600
  syntax clear
elseif exists("b:current_syntax")
  finish
endif

if !exists("main_syntax")
  let main_syntax = 'sh'
endif

if version < 600
  so <sfile>:p:h/sh.vim
else
  runtime! syntax/sh.vim
  unlet b:current_syntax
endif

syntax case match

syn keyword rcconfKeywordYes YES
syn keyword rcconfKeywordNo NO

let b:current_syntax = "rcconf"

hi def link rcconfKeywordYes Type
hi def link rcconfKeywordNo Special

This worked before, but now in vim 8 it works only if there are spaces between keywords and other symbols:

name = YES
anothername = NO

Answer 1

It could depend on iskeyword value.
keyword only matches for a complete word, for example, if you define the keyword NO, it will not match NOT or PIANO.
If Vim considers = is a letter, then anothername=NO is a single word, and it's not NO.

You can check if Vim considers = to be a letter with :set iskeyword?.
You can probably fix it: with the command :set iskeyword-==, YES and NO will get colors.
With :set iskeyword+==, they lose they colors again.

You can also use the syntax iskeyword instead (it's not the same, for example it doesn't change abbrev behavior, and it is recommended to use this one).
It's explain at :help syntax|3546.
Try with: :syntax iskeyword @,48-57,192-255,$,_.

I don't know which one breaks your syntax, so you can try both.