It's the "ht" in http & html
The tab mechanism also came into its 
own as a rapid and consistent way of uniformly indenting the first line of each... [DOC] [TLE] 24.5. turtle  Turtle graphics for Tk  Python 2.7.12 documentation [PAR] Its constructor needs a Canvas, ScrolledCanvas or TurtleScreen as argument, so 
the RawTurtle objects know where to draw.