Class representing a set of pages in a paginator. You can subclass this to customize it if you wish!
Default page group, if you have more than one.
All groups of pages stored in this class.
Add a page to the default group.
Add a page to a given group.
Retrieve the page at the given index, from the default group.
Retrieve the page at the given index, from a given group.
Check that this Pages object is valid, throwing if it isn't..