do we need parse tree modification routines?

If we allow patterns, we can also allow tree construction from input snippets. Should we add routines to replace parse tree nodes?
Ter

The issue proposes patterns, tree construction from input snippets, and routines to replace parse-tree nodes, but it names no files, tests, or entry points. First determine whether these capabilities fit ANTLR's existing parse-tree design and identify the relevant implementation and test locations. Done would require an agreed scope and design rather than an isolated edit.

Written by the indexing model from the issue text.