<?php

header('Content-Type: text/plain; charset=utf-8');

$show_borken = !!0;

#begin_omit

$myself = file_get_contents("regexes.php");
$single = 'This line has [OMIT]some words[/OMIT] omitted [OMIT]twice[/OMIT].';
#==> “This line has  omitted .”
$nested = 'on [OMIT]this line, [OMIT]you have[/OMIT] to [/OMIT]count';
#==> “on count”
$multi  = "this [OMIT] line\ndoesn't have [/OMIT]omissions";
#==> “this [OMIT] line\ndoesn't have [/OMIT]omissions”

#begin_omit
$lines = array( 'single', 'nested', 'multi' );
#end_omit

### Single-line exclusion. ###

$single_pat =
    '@\\[OMIT\\](.*?)\\[/OMIT\\]@i';
$nested_pat =
    '@\\[OMIT\\]((?:(?R)|.)*?)\\[/OMIT\\]@i';
$multi_pat =
    '@\\[OMIT\\]((?:(?R)|.)*?)\\[/OMIT\\]@is';
$pats = array( 'single_pat', 'nested_pat', 'multi_pat', );

foreach ($pats as $pv)
foreach ($lines as $lv)
if ($show_borken or $pv == $lv . '_pat')
    printf("---%s[%s]---\n%s\n↓\n%s\n\n",
           $lv, $pv, $$lv,
           preg_replace($$pv, '', $$lv));
#end_omit


### C-like preprocessor. ###
$pp_pat = <<<END
    ( ^ [#] \s* begin_omit \s* $ )
    ( (?: (?R) | . )*? )
    ( ^ [#] \s* end_omit \s* $ )
END;
echo preg_replace("@$pp_pat@msx", '', $myself);