How to define a circle shape in an Android XML drawable file

Question

I'm having some trouble locating the Android shape definitions in XML documentation. In order to integrate it in my layout files, I need to describe a straightforward circle filled with a solid colour in an XML file.

Sadly, the XML attributes of the Shape classes are not covered in the documentation on android.com. Although there is no description of how to determine the size, colour, or angle required to build a circle out of an Arc, I believe I should use an ArcShape to draw a circle.