Is it correct practice to always capitalize kwargs if I provided a default? So the param would be `Value=None`?

Decoupling it seems good for the prefix.

`cast_value` is also used in the `_input_handler` so private won't make sense, moving the rest of that code into the method will also cause a less obvious requirement between the type of data it receives which would need to be FieldStorage. I feel that falls outside of what an HTMLInputOption needs to be aware of.