Start -> BOX | TWO_BOXES
BOX -> rectangle
BOX -> contains(rectangle, circle)
TWO_BOXES-> left_of(BOX, BOX)
You add grahpical description rules of cirlces or rectangles that satisfy the above grammar. For example
rectangle 0 0 100 100
circle 0 0 100 100
rectangle 150 0 250 100
then press on submit and if the input is valid it will be drawn in the canvas.
You can open and try the project by either opening index.html file or check the online demo