Looking at RegexPart.java in layer0/bnf I note "regex cannot contain sub-elements" and the BNF grammar schema shows only the "type" attribute.

So the kind of explicit regex processing in NK3 is gone in NK4. If regex processing is used in that fashion it would be implemented through an endpoint service with implementation in Java, Groovy or one of the other langs, along the lines of your "active:toUpper" examples.

Also, DPML in NK4 can no longer do regex processing explicitly since <regex> has no sub-elements?

Just checking some NK3 -> NK4 changes.