As linhas necessárias são as seguintes:
" Include PHP highlighting between **phpbegin** and **phpend** tags
syn include @notesPHP syntax/php.vim
syn region phpCustom start=+\*\*phpbegin\*\*+ keepend end=+\*\*phpend\*\*+ contains=@notesPHP
" Include JavaScript highlighting between **jsbegin** and **jsend** tags
syn include @notesJavaScript syntax/javascript.vim
syn region javaScriptCustom start=+\*\*jsbegin\*\*+ keepend end=+\*\*jsend\*\*+me=s-1 contains=@nJavaScript