code: function CommandAssignment(requisition) {
    var commandParamMetadata = {
      name: '__command',
      type: { name: 'command', allowNonExec: false }
    };
    // This is a hack so that rather than reply with a generic description of the
    // command assignment, we reply with the description of the assigned command,
    // (using a generic term if there is no assigned command)
    var self = this;
    Object.defineProperty(commandParamMetadata, 'description', {
      get: function() {
        var value = self.value;
        return value && value.description ?
            value.description :
            'The command to execute';
      },
      enumerable: true
    });
    this.param = new Parameter(requisition.system.types, commandParamMetadata);
  }
docs: This is a special assignment to reflect the command itself.