Essential input elements of a gui toolkit

I am in a process of designing a new toolkit for mobile devices (as a part of my Master's thesis). I would like to know if there is some theoretical backgroud (researches, books, tutorials, etc...) to what a toolkit should contain.

Intuitively, things like buttons, input fields, sliders, switches, etc... should be there. But why? It would make me uneasy to just write these things in my thesis without any reference.