rxpy.graph: Graph nodes represent the regular expression, something like an AST or
set of opcodes (they are intended to match individual operations in the
engine).
rxpy.graph.opcode: Nodes in this module are present in the final output from the parser.
rxpy.parser.replace: Additional parser code for the expressions used in re.sub and similar
routines, where a "replacement" can be specified, containing group references
and escaped characters.