general_value_spec

general_value_spec 
      ::= 
      parameter_spec 
      | dyn_parameter_spec 
      | variable_spec 
      | "user" 
      | "current_user" 
      | "session_user" 
      | "system_user" 
      | "value" 

This rule is called by

-> unsigned_value_spec
-> value_spec