Sa i'n question

I hear it a lot watching S4C. Is it pretty much a catch all negative spoken phrase? Sa i’n mynd i’r parc, sa i’n hoffi coffi, sa i’n siarad llawr o Gymraeg etc etc or are there specific rules in terms of when you can and cannot use it?

There aren’t specific rules as such, but it’s a form more commonly used in the South than the North.

It is one of those things that doesn’t tend to get taught in formal classes, so

would probably tend to raise eyebrows and be considered to be somewhat oxymoronic!