Class Definitions pop-over

[thorade]

The Class Definitions pop-over is the same as the Builtin Types pop-over. The text should be changed, but I am unsure what to use instead (would have sent a pull request otherwise). Maybe link to Chapter 7: Inheritance, Modification and Redeclaration.

[xogeny]

Good catch. I never noticed this.

I would suggest either Chapter 4 or Section 4.5.