You are not going to find a specific section of the tax code that deals with that section of schedule A. Its a "catch-all" section of a form that allows people to list all kinds of things that are addressed in many different sections of the tax code.
Basically, it is a section for the listing of expenses of making money, that would not be listed elsewhere on a tax return.
Its no different than line 21 "other income" on the front of the tax form. There is no single code section that deals with that either, because again, its a "catch-all" section of the form.
Without those types of sections being available, tax returns would be hundreds of pages long.

