Selectbox key argument purpose is unclear

[rq-aszasz]

Link to doc page in question (if any):
https://github.com/streamlit/docs/blob/main/content/library/api/widgets/selectbox.md

Name of the Streamlit feature whose docs need improvement:
Selectbox

What you think the docs should say:
It is not clear how the key argument is useful. When would one use it and why?
Please include an example.

[MathCatsAnd]

I've written an extended explanation of how widgets work, including the purpose of keys. #643

If that draft is approved (or some version of it), would it make sense to link to the explanation about keys from each widget's docstring re: the key parameter since it is more involved to describe than what would fit nicely there...

[rq-aszasz]

I support your proposal @MathCatsAnd, thanks!

[sfc-gh-dmatthews]

The page about widbet behavior has been published and includes an explanation on keys. Remaining todo is to review the description given for keys and include a helpful link. This may relate to building a list of standard parameters that are shared across functions which is also planned, so I'll leave this open until I circle around to that.