#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)(?<=<)(?!\/|\?)"
Local $sString = "<?xml version="1.0" encoding="UTF-8"?>" & @CRLF & _
"<mediabericht xmlns:mb="http://www.mediabericht.org"><inhoud>Randominhoud 22</inhoud><netwerk>Twitter</netwerk><datum>1408625886036</datum><film>Gladiator</film></mediabericht>"
Local $sSubst = "mb:"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm