"Correct regEx in expression builder not accepted"

By chance I found that it works with double escape characters: 

Though the question remains, why this particular editor expects \\ instead of \ ? 

Thanks. 

Hi @kypexin - so I have found that the online RegEx expression testers are usually running JavaScript, which appears to sometimes parse expressions differently than Java (which is how RapidMiner does it).  Don't ask me why.  I think Ingo posted something about this a while ago...

Scott

Yes, it's just different implementations of regex.  In the java version, the "\" is a special character so it needs to be declared with the special escape character for that, which also happens to be "\".  That's why you need "\\".  If you were wanting to use other regex special characters (like ?,+,., etc.) you would also need to preface them with "\" in RapidMiner.  So it's not the doubling of the character that matters, just the preface with "\".

Thank you guys for sharing some secret knowledge