Simplify the following text for a Grade 13 native English-speaking person.
Original: Principle 18 of the Yogyakarta Principles , a document about international law on human rights insists that `` any classifications to the contrary , a person 's gender identity is not in and of itself , medical condition '' .
Simplified: The Yogyakarta Principles , which is a document on application of international human rights law , provides definition on gender identity .