#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?:src|action|href)=[\'"]\K/(?!/)[^\'"]*"
Local $sString = "<img src="/relative/url/img.jpg" />" & @CRLF & _
"<form action="/">" & @CRLF & _
"<form action="/contact-us/">" & @CRLF & _
"<a href='/relative/url/'>Note the Single Quote</a>" & @CRLF & _
"<img src="//site.com/protocol-relative-img.jpg" />" & @CRLF & _
""
Local $sSubst = "https://example.com$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