Extra Spells

The description would be more helpful if it told me whether this feat is class or spell list specific.  Is it meant for any caster, or certain classes.  What spell lists does it draw from?  Does it let you set parameters for each to prevent players from accidentally picking something they shouldn't be able to?  I appreciate the thought but please give me some of the guidelines to work from before I apply this to a character.

Thank You.

It is any spell, from any list, available to any class and any race. It is for if people have somehow learned extra spells like with Caleb Widogast learning Dunamanctic magics from shadowhand Essek.