neovim/runtime/syntax/plp.vim

" Vim syntax file
" Language:	PLP (Perl in HTML)
" Maintainer:	Juerd <juerd@juerd.nl>
" Last Change:	2003 Apr 25
" Cloned From:	aspperl.vim

" Add to filetype.vim the following line (without quote sign):
" au BufNewFile,BufRead *.plp setf plp

" quit when a syntax file was already loaded
if exists("b:current_syntax")
  finish
endif

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

runtime! syntax/html.vim
unlet b:current_syntax
syn include @PLPperl syntax/perl.vim

syn cluster htmlPreproc add=PLPperlblock

syn keyword perlControl PLP_END
syn keyword perlStatementInclude include Include
syn keyword perlStatementFiles ReadFile WriteFile Counter
syn keyword perlStatementScalar Entity AutoURL DecodeURI EncodeURI

syn cluster PLPperlcode contains=perlStatement.*,perlFunction,perlOperator,perlVarPlain,perlVarNotInMatches,perlShellCommand,perlFloat,perlNumber,perlStringUnexpanded,perlString,perlQQ,perlControl,perlConditional,perlRepeat,perlComment,perlPOD,perlHereDoc,perlPackageDecl,perlElseIfError,perlFiledescRead,perlMatch

syn region  PLPperlblock keepend matchgroup=Delimiter start=+<:=\=+ end=+:>+ transparent contains=@PLPperlcode

syn region  PLPinclude keepend matchgroup=Delimiter start=+<(+ end=+)>+

let b:current_syntax = "plp"