When input parameters are optional or can have default values, use the PROC statement to assign the parameters to variables by name rather than by position. Such parameters (keyword parameters) must match a variable name that you specify on the PROC statement. See item 5 for special rules on naming variables specified on the PROC statement. The PROC statement can accept keyword parameters with or without values.

Keyword parameters and their matching variables have up to 31 alphanumeric characters (A-Z, 0-9, #, $, @). Keyword parameter values have the same length restriction as symbolic variable values: 32768 bytes.