| ``none'' | variable has no type |
| ``scalar'' | variable is a scalar number |
| ``complex'' | variable is a complex number |
| ``string'' | variable is a string |
| ``array'' | variable is an array |
| ``zoidlist'' | variable is a zoidlist |
| ``layer_expr'' | variable is a layer_expr |
| ``handle'' | variable is a handle to something |