Function globals canvas MapStructure DotSym new

For the instances returned from makeinstance:
@param group The #Canvas.Group to add this to.
@param layer The #SymbolLayer this is a child of.
@param model A correct object (e.g. positioned ghost) as
expected by the .draw file that represents
metadata like position, speed, etc.
@param controller Optional controller "glue". Each method
is called with the model as the only argument.