SpellHasCastingPerk

This function was designed specifically for specific perk entry points that allow you to define conditions for spells, to support the "Casting Perk" option on spells. The function checks whether the reference it's being run on has a spell as a base form and, if so, whether the spell's casting perk is equal to the parameter perk. The condition returns 1 if so, or 0 otherwise.

It is ordinarily not possible for a reference to have a spell as its base form. This can happen specifically when using certain perk entry points: the Mod Spell Cost entry point, for example, creates a dummy/throwaway reference, sets the spell as its base form, and runs the condition on it, such that "the spell" is the condition's "Subject." Thus by using this condition function specifically in that entry point, and having it run on "Subject," you can limit a perk's entry points to apply only to spells that have been tagged with some specific perk.