Confusion between unix-word-rubout and backward-kill-word

GNU Readline has commands:

• unix-word-rubout (bound to C-w = Ctrl+W by default) kills the word before point, using white space as a word boundary;
• backward-kill-word (bound to M-DEL = Alt+Bksp by default) kills the word before point, using “not a letter nor a digit” as a word boundary.

The difference between these two commands is very useful. For example, suppose I have typed:

some-command --some-option /some/very/long/path

then realize that the path is wrong. I can then erase the entire path by pressing Ctrl+W, or erase it part-by-part by pressing Alt+Bksp.

However, prompt_toolkit binds both unix-word-rubout and backward-kill-word to the same action, which behaves more like backward-kill-word but not exactly (e.g. considers underscores as parts of words), and then binds both Ctrl+W and Alt+Bksp to unix-word-rubout by default.

Is there any specific reason for this divergence from Readline? Would you consider making prompt_toolkit behave the same as Readline here?

Start in prompt_toolkit/key_binding/bindings/named_commands.py around the unix-word-rubout and backward-kill-word bindings cited in the issue. Compare their actions and the default Ctrl+W and Alt+Backspace bindings with the Readline behavior described; done means the two commands and defaults have the intended distinct behavior, with supporting tests if the project has them.