SCPI standard states that some nodes in SCPI commands tree may play role of default nodes. That means that it is not required to specify them in command headers. Same applies for arguments. In this manual optional nodes and arguments are denoted with square brackets.

For example, let’s consider the following syntax description: :FETCh[:SCALar]? [<series name>]

Here square brackets indicate the fact that the node inside them (SCALAR) is default node under its parent node (FETCH). That means that you can specify the header as: :FETCH or :FETCH:SCALAR and result will be same. Same applies for parameters in square brackets. In this syntax <series name> parameter is marked as optional. Exact behavior of a command with omitted parameter is specified separately for each command.