Additional "Class Reference" sections to docs please

Prior to version 4 certain classes (e.g. Model) did not need a "Class Reference" because... well , there wasn't much to reference. However, the Model class in v4 is rich with functionality. While most (all?) of the available methods get discussed somewhere in the documentation nothing beats a comprehensive, single-location reference.

In addition to Model, the Entity and Validation classes would benefit from Class Reference sections.

There might be other classes too, but those three jump out at me.