A label is an alphabetic character string used to name lines. It is especially useful for keeping track of a line whose relative line number may change because labels remain set on a line even when relative line numbers change. The special labels shown are automatically assigned by the editor. A label must begin with a period (.) and be followed by no more than 8 alphabetic characters, the first of which cannot be Z. No special characters or numeric characters are allowed.

The special labels that are automatically assigned by the editor all begin with the letter Z. Labels beginning with Z are reserved for editor use only.