The document discusses the vocative case in grammar. The vocative is a nominal element added to a sentence to refer to the person being addressed. It can occur initially, medially, or finally in a sentence. The vocative may take several forms, including a single noun with or without a title, the pronoun "you", terms of family relationship, endearments, titles of respect, marks of profession or status, nominal clauses, or a noun with modifiers. Examples of each type of vocative are provided.