正则表达式除了字符串+组的使用

Question

I'm trying to make a whitelist of html tags, here's my code :

$string = "<x>-<x>";
$result = preg_match('#^<(?!white1|white2)>.*<(\1)>$#i', $string);

But it returns false, and I don't know why. I simplified the regex to avoid confusions, but this is still the same idea.

I want to match every correct tag but the ones I want to keep safe. This regex will go on a preg_replace to erase every matched tag and let the ones I allow.

Thanks for your help in advance !

EDIT: If I find a way to do this with regexs, I'll put the solution here. But for now, I'll do it with strip_tags().

EDIT2: The easiest way I thought to is to parse all the tags and then revert back the ones we allow.

Answer 1

If you want to eliminate unwanted tags, you can use strip_tags:

$allowedTags     = '<p><a><img>';
$filteredContent = strip_tags($content, $allowedTags);