Class ParseTreeProperty

In the API for the runtime, as documented for Java in https://www.antlr.org/api/Java, we have a Class ParseTreeProperty in the Tree-package. It is to easily attach a value to a node in the parse tree. Java uses an IdentityHashMap for that, with the node / parse tree as key. In PHP we don't have such a datastructure, where we can use an object as key. That is probably why you left this class out in the PHP runtime?

My thoughts:
* to make it compatible with the general runtime API, we can implement another way to associate values with a node. Maybe using spl_object_id or spl_object_hash as a key/identity for the node.
* or do it the dirty PHP-way, where we can add values to any object: adding values directly to the node. Disadvantage: you change the tree, which might give problems if you want to reuse the tree for multiple applications (multiple listeners / visitors using the same tree).
My preference is option nr. 1, as it conforms the general API. Shall I make a proof of concept?

Maybe I'm overlooking something here and is this a non-issue... Please let me know your thoughts.

Start with the linked Java API documentation for ParseTreeProperty and inspect the PHP runtime's Tree package for the missing entry point. The issue presents two incompatible implementation approaches but names no files, tests, or acceptance criteria; done requires maintainers to choose and specify a compatible design before implementation.

Written by the indexing model from the issue text.