#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "<body[^>]*>"
Local $sString = "<body class="wordpress y2015 m10 d23 h12 single s-y2010 s-m02" style="width: 100%;">" & @CRLF & _
"<body class="s-category-linux" style="background-color: red;">" & @CRLF & _
"<body class="wordpress y2015 m10 d23 h12 single s-y2010 s-m02 s-d10" style="width: 100%;"><div id="wrapper"><div id="header">"
Local $sSubst = "$0<mynewtag>"
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