Probably one of my favourite Welsh words, difficult for learners to say and doesn't quite match up with any English word. Also, I don't really understand the rules for it's use. Is it basically an emphatic pronoun?
It seems to be used alongside rather than instead of ti in the North. I'm not 100% if they're interchangeable. Excuse my ignorance.
They're both used in the North, but the North is a large area, some areas use ti and some use chdi but everyone is aware of both.