(By Hannah J. Haynie): "This feature identifies languages that do not require a phonologically overt S or A argument expressed by a noun phrase or phonologically independent pronoun when the referent can be inferred from context. These languages are often called ‘pro-drop’ languages, and the phenomenon is generally referred to as ‘null anaphora’ or ‘zero anaphora’.
Here ‘omitted’ means phonologically unexpressed (we do not intend for this feature to make any distinctions regarding the theoretical status of a null argument). To count as 1, pro-drop should occur where the S or A argument might otherwise be expressed by an independent pronoun or full noun phrase. Specifically, pro-drop should occur in simple, declarative main clauses.
Pro-drop is not mutually exclusive with indexing of the S or A argument on the verb. If, in the absence of an independent pronoun or nominal S or A, there is indexing of this argument on the verb, you may still code 1.