What language is indesign's regular expressions in?

[dublove]

Feels a lot like perl's, and occasionally a little different from js's?

I downloaded a RegexBuddy and tried it but it didn't recognize ~K.

It's so sad that so many people only know each other.
Don't recognize \l\u.

[Barb Binder · Accepted solution]

"InDesign uses the Boost libraries for GREP; information on those libraries is available from http://www.boost.org, though the documentation there is a bit sparse."

—GREP in InDesign, Third Edition by @Peter Kahrel 

If you haven't purchased this book yet, @dublove, I highly recommend it.

~Barb

[dublove]

Thanks Barb Binder
I found boost:regex 1.78-1.83 now.
Also, I found that Editpad 8 is also very much like ID's regular.