RegEx help

I've managed to get this:
echo preg_replace('/<(\S):(\S)(.*)>/msiU', '<\\2\\3>', '<blah:blah test="test: this">');

However, that doesn't remove anything. What it should output is:
<blah test="test: this">

echo preg_replace('/<(?:[a-zA-Z]+:)/m', '<', '<blah:blah test="test: this">');
remember to use htmlentities so your browser doesn't render while testing (or view the source).

What does that "?:" do?

What does that "?:" do?

it means it is non capturing unlike just using normal parentheses(capturing) which will give you the \1 and so on.

Ah, OK. Thanks.