Quick search:

What is a static instance

A static instance is an instance that only changes if the code that created it is changed.
Static instances are usually created from scratch by a static method. They can be used as categories. An example is example3.Gender.

PntClassDescriptor supports the retrieval of instances from static methods. This is the default behavior of options of derived properties whose type is not a subclass of PntDbObject. EditDetailsPages will show a select widget the user can choose from. See example 3.

Static instances can also be used for delegation. The way they are created is the same, but they will be usually instances of different subclasses. When an object references one, it can partially behave like that one, if it references another, it can partially behave like the other. This can be used as a workaround for the single inheritance limitation of php.