Phrase structure rules regulate the arrangement of elements that make up phrases. The rules stipulate the position of specifiers, heads, and complements for noun phrases (NP), verb phrases (VP), adjective phrases (AP), and prepositional phrases (PP). For example, an NP can consist of a determiner, noun, and prepositional phrase complement, or just a determiner and noun. Phrases may contain various combinations of specifiers, heads, and complements.