The action calls the lua function specified with action. The function should be
implemented above the call to Tool.register.
The first argument to the function is self, the instance of the
custom tool class.
Supported argument types are "bool", "number", and "string".
Note
Arguments can only be used when calling an action from the Command channel,
they will not be set when calling an action from a button in the user interface.
It is recommended to set ui=false for actions with arguments.