[note] Q: Why do some diagrams and models contain so many static public methods and basically fully static "Helper" and "Builder" Classes with only a few instantiated objects ? A: It's an interim step for progressive migration to classes and objects.

CASE: build an editable AJAX form enabling the applicability of each Flag by entity type and bundle name to be seen and set in a table, with an AJAX entity type filter.

Also not bad except for those horrible long operations in the include file  flagplus.flags.inc, which is a a typical consequence of lack of OOP, and of Drupal7's system for passing arguments to non-OOP callbacks functions (unless you like shoving it all into an unstructured "$options" array as so often done in Drupal, which is also rather blech and yuck).

Notice how, compared with the non-AJAX form case, the entity filter sub-form is handled a bit differently; instead of it being built with a default from a system variable it is built using the form state value from the AJAX callback.