#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?miu)(<p[^>]+")([^>"]+)"
Local $sString = "<p id="tem" style="text-align: justify;"><span style="font-size: 11pt;">hello world<br /></span></p>" & @CRLF & _
"<p style="text-align: justify;">test</p>" & @CRLF & _
"<p > </p>" & @CRLF & _
"<p> </p>"
Local $sSubst = "$1$2margin:0;"
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