I have tried to simplify as much as the possible the work need to develop a new re package replacement. If you want to implement a new matching algorithm you should:
RXPY includes a simple interpreter-based engine in the package rxpy.engine.simple.
RXPY is in active development and any aspect of the design may change. The general architecture is likely to be fairly stable, but new flags and opcodes are inevitable. Since there is currently only one engine, the engine related API is an area that is unlikely to be sufficiently generic and, therefore, particularly like to require adaptions.
At some point (once more engines exist), I hope to make the rxpy.re module select the “best” engine for particular patterns.