What is canvas in APP Lab ?if I can get details of all elements available in App Lab

My student asked me about Canvas in App Lab.I could not find any answer for that in App Lab documentation.
Where should I be looking up for more information on elements in App lab?
Thank you ,

Canvas is sort of a way to draw in App Lab. It is different from turtle drawing, and allows them to display shapes on the screen. It will not appear in most levels (they only show the required tools for that level’s task) but can be found in an applab sandbox. Documentation and some examples are available here.