#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)<([^>\s]+)[^>]*>(?:\s*(?:<br \/>| | | | | | | )\s*)*<\/\1>"
Local $sString = "<div> " & @CRLF & _
" <h1>This is a html structure.</h1> " & @CRLF & _
" <p>This is not empty.</p> " & @CRLF & _
" <p></p> " & @CRLF & _
" <p><br /></p>" & @CRLF & _
" <p> <br />  </p>" & @CRLF & _
" <p> </p> " & @CRLF & _
" <p> </p> " & @CRLF & _
"</div>"
Local $sSubst = ""
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