#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?s)Keyword(?=[^><]*<\/p>)"
Local $sString = "<div>" & @CRLF & _
" <img />" & @CRLF & _
" <span>Foo Bar - Keyword</span>" & @CRLF & _
" </div>" & @CRLF & _
" <h2>Keyword - Foo Bar</h2>" & @CRLF & _
" <p>Lorem Ypsum, Keyword, Lorem Pysum.</p>" & @CRLF & _
" <h2>Heading - Keyword</h2>" & @CRLF & _
" <p>Lorem Ypsum, Keyword, Lorem Pysum.</p>" & @CRLF & _
" ..."
Local $sSubst = "<em>$0</em>"
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