Operand1 is the left operand. Operand1 can be any of the following:
The user-assigned A to Z and AA to ZZ collect vector variables. The collect vector variable can be either local or global.
The system-assigned A to Z and AA to ZZ vector variables, such as ani, asaiuui, and doy.
V1 to V9 VDN variables.
digits: The collected digits buffer for the current contents of the call.
none: A keyword denoting a null or empty string for a string operator, or a 0 for an arithmetic operator.