#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?i)((?:(?!<[/]mark\s*>).){0,5})<mark\s*>([^<]*)<[/]mark\s*>(?=((?:(?!<mark\s*>).){0,5}))"
Local $sString = "Lorem ipsum mark> <MARK >dolor</MARK > < mark sitamet. <mark>Lorem</mark> ipsum again and <mark>dolor</mark>." & @CRLF & _
"" & @CRLF & _
"um <mark>dolor</mark> sit amet. <mark>Lorem</mark> ipsum again and <mark>dolor</mark>." & @CRLF & _
"" & @CRLF & _
"um <mark>dolor</mark> sit <test amet. <mark>Lorem</mark> ipsum again and <mark>dolor</mark>." & @CRLF & _
"" & @CRLF & _
"Lorem ipsum <MARK >dolor</MARK > sit <mark>amet.</mark><mark>Lorem</mark> ipsum again and <mark>dolor</mark>."
Local $sSubst = "\n$1 $2 $3\n"
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