Malcolm is right about the spelling, and the history.
Tunesmith is right about the lack of information.
Most of the reason is that it is very much played by ear. If you want to play like Hazel Wrigley, buy a lot of CDs, listen to them, but above all practise (learn how to 'hear' as much as how to play, and be committed to do so for a long time)
It's not stuff that can be transmitted via a book.