get_visible
Description:
Returns true if the mark is visible.
A cursor is displayed for visible marks.
Parameters:
| this | 
           a `GtkTextMark`  | 
      
Returns:
| 
           true if visible  | 
      
Returns true if the mark is visible.
A cursor is displayed for visible marks.
| this | 
           a `GtkTextMark`  | 
      
| 
           true if visible  |