#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)(?<=id=")([^"\n]+)"[^#\n]+#\K"
Local $sString = "<li><a id="a4.9" href="trigger_marker.html#">Trigger marker</a> </li>" & @CRLF & _
"<li><a id="a4.10" href="timedelayarrow.html#">Time-delay arrow</a> </li>" & @CRLF & _
"<li><a id="a4.11" href="spectrumview.html#">Spectrum view</a> </li>"
Local $sSubst = "\1"
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