Docs: Clarify that `register_taxonomy()` only accepts lowercase values for the `$taxonomy` parameter

[audrasjb]

This issue was pointed out by @bengreeley in a DevHub User Contributed note:

Both register_taxonomy() and register_post_type() have a known bug where the taxonomy or post type name needs to be lowercase to work properly (see #16600).

This page mentions lowercase [JB: `register_taxonomy` devhub page] in 'Additional Parameter Information', which is buried a bit deeper on the page. I'd recommend to update this page to include language such as "may only contain lowercase alphanumeric characters" in the main parameter section for $taxonomy, similar to the way it's added for register_post_type() at ​https://developer.wordpress.org/reference/functions/register_post_type/

Since using anything but uppercase can lead to serious issues that have yet to be resolved I think making this more obvious would be beneficial to the end user.

[dipakparmar443]

I have update the inline document in attached patch file

[dipakparmar443]

Desc: updated patch

[audrasjb]

Thanks for the patch @dipakparmar443! Looks like there is a small typo: "Must" should be lowercase as it follows a comma :)

[dipakparmar443]

Please check latest update patch

[dipakparmar443]

@audrasjb Please check latest update patch

[audrasjb]

Looks good to me, thank you 👍

[audrasjb]

In 53873:

Docs: Clarify that register_taxonomy() only accepts lowercase values for the $taxonomy parameter.

This brings consistency with docblock used in register_post_type().

Props audrasjb, bengreeley, dipakparmar443.
Fixes #56352
See #55646.