ref: a7bbd897fc6be13b8699a206dd422ad6e09928d3
dir: /html/rect.html/
docname=rect:Rectangles <p> Draw lines along the grid edges to divide the grid into rectangles, so that each rectangle contains exactly one numbered square and its area is equal to the number written in that square. <p> Click and drag from one grid corner to another, or from one square centre to another, to draw a rectangle. You can also drag along a grid line to just draw a line at a time, or just click on a single grid edge to draw or erase it.