A positive setting of the parameter allows an empty pro-element to be identified by its governor, which is the case in pro-drop languages.
[1] A term used in government-binding theory for a specification of the types of variation that a principle of grammar manifests among different languages.
The overall approach has been called the principles and parameters theory (PPT) of universal grammar, and has since come to be applied outside of syntactic contexts, notably in characterizing phonological relations.
For example, the question has been raised: How do children ‘set’ a UG parameter to fit their particular language?
[3] In government-binding theory, any of the various putative universal statements permits a specified degree of variation within languages.