gh-139489: Add xml.sax.saxutils.is_valid_name()

[serhiy-storchaka]

It allows to check whether a string can be used as an element or attribute name in XML.

• Issue: Add utility functions to test for legal XML characters and names #139489

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📚 Documentation preview 📚: https://cpython-previews--139768.org.readthedocs.build/

[picnixz]

Suggested change

	* Add the :func:`~xml.sax.utils.is_valid_name` function, which allows to check
	* Add the :func:`~xml.sax.saxutils.is_valid_name` function, which allows to check

While sax.utils exists, the documented module is saxutils.

[serhiy-storchaka]

Thank you for noticing. More changes there were needed.

[vstinner]

Why not adding the function in the xml package level, for example in a xml.utils module?

The function doesn't seem to be specific to the sax implementation. Is it?

[serhiy-storchaka]

There is no an xml.utils module.

[vstinner]

There is no an xml.utils module.

I'm suggesting to create such xml.utils module. Ok maybe put the new function directly in the xml top-level package?

[serhiy-storchaka]

This is an interesting idea.