Model: some doc fixes

Basically I was trying to understand everything around getActualFields method and added some comments.
As result I slightly modified this method (strtolower, just in case and so).
And also "normalized" some comments of this particular method and also some near by methods.

I guess it could be useful to merge in and continue work on docs/comments later on.
Merge pull request #269 from DarkSide666/patch-1

Model: fixes