Correct xml:lang value for Pinyin Chinese vs Simplified Chinese

Hi.

I am faced with with content that shows three variants:
1. a transliteration of the phrase in Pidgin/Pinyin
2. The phrase as written with Chinese Simplified characters
3. An even more simple transliteration with English characters, but no
accents etc..

The dialect of the language is Mandarin

Question is how do I express most of the above with xml:lang so that
software down the line (such as browsers) can do something useful with
it?

From what I've seen, one can be pretty descriptive in the attribute,
but it is interesting what the tools support.
I am happy with the middle ground such as "zh-Hans", but I would also
want to differentiate between the different transliterations of the
same phrase.
Is that beyond the scope of xml:lang attribute?


Regards,

Lech