How does kate / kwrite store text internally

Mostly out of idle curiosity, I'd like to find out how kate / kwrite store text 
internally -- I mean a gapped buffer, a piece table, some (other) kind of tree, 
...

For extra credit ;-) is there any document that tells how that was decided and 
/ or compares it to alternate methods?

(Aside: Scintilla uses a gapped buffer with some auxillary structures (like a 
separate style buffer, maybe others), Iiuc, Microsoft Word uses some kind of 
tree.)

I have tried some Google searches, but no luck so far.

Thanks!