Support XPATH function substring-before,substring-after,translate

[oocllanlo]

Hi dear author, we are doing migration from XPATH to JSONPATH, we are facing some old XPATH expression that with some function that JSONPATH doesn't have, may i know any plan to support title mentioned functions? or open a customerize interface that let user customize FUNCTIONS? now PathFunctionFactory cannot being modified. that would be greate if can support it.