#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?ms)\[\?\](?:(?!\[/?\?\]).)*%empty%(?:(?!\[\?\]).)*\[/\?]"
Local $sString = "[?]<h1>%empty%</h1>" & @CRLF & _
"<p>text</p>" & @CRLF & _
"[/?] " & @CRLF & _
"text " & @CRLF & _
"[?]<h1>%empty%</h1>" & @CRLF & _
"<p>text</p>" & @CRLF & _
"[/?] " & @CRLF & _
"text" & @CRLF & _
"" & @CRLF & _
"" & @CRLF & _
"" & @CRLF & _
"[?]<h1>%!empty%</h1>" & @CRLF & _
"<p>text</p>" & @CRLF & _
"[/?] " & @CRLF & _
"text " & @CRLF & _
"[?][][/<h1>%empty%</h1>][][[[]]]" & @CRLF & _
"<p>text</p>" & @CRLF & _
"[/?] " & @CRLF & _
"[?]<h1>%empty%</h1>" & @CRLF & _
"<p>text</p>[?]" & @CRLF & _
"[/?] " & @CRLF & _
"text[?]<h1>%!empty%</h1>" & @CRLF & _
"<p>text</p>" & @CRLF & _
"[/?] "
Local $sSubst = "REPLACED"
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