forward-word doesn't quite match emacs/readline, and isn't configurable

Consider a(123), with the cursor at a. In both emacs and readline, M-f moves forward one character, to the (. In prompt-toolkit, it moves to the 1.

It also would be nice to be able to configure word boundaries. In particular, I would like to be able to make it so that AbcDef and abc_def are both treated as two words for the purposes of word movement/deletion. The current approach does a regex search, but I believe you need to tokenize the input.

Also worth noting that the docs for forward-word state that words are composed of letters and numbers, but the implementation includes underscores as well (and that behavior in particular does not match readline and is quite annoying).

Start with prompt_toolkit/key_binding/bindings/named_commands.py, especially the documented and implemented forward-word behavior. Compare its movement with emacs and readline for examples such as a(123), then determine how configurable boundaries should handle underscores and camel-case text. Done means word movement and deletion match the requested boundaries and the documentation matches the behavior.