#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?i)\b(i|em|b)(\w*)\/(i|em|b)\b"
Local $sString = "{"query":"incessant","sourceLanguage":"en","targetLanguage":"en","primaries":[{"type":"headword","terms":[{"type":"text","text":"in·ces·sant","language":"en","labels":[{"text":"Adjective","title":"Part-of-speech"}]},{"type":"phonetic","text":"/inˈsesənt/","language":"und"},{"type":"sound","text":"http://www.gstatic.com/dictionary/static/sounds/de/0/incessant.mp3","language":"und"}],"entries":[{"type":"meaning","terms":[{"type":"text","text":"(of something regarded as unpleasant) Continuing without pause or interruption","language":"en"}],"entries":[{"type":"example","terms":[{"type":"text","text":"the emincessant/em beat of the music","language":"en"}]}]}]}]}"
Local $sSubst = "$2"
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