The close line play area is an area of the field, tackle to tackle, 2 yards behind and beyond the line of scrimmage. In this area, linemen hit quite a bit, and blocks below the waist are legal. However, unneccesary roughness acts are still penalized.
Also note that in the last paragraph, the incorrect article is referenced. 5.5.1 should be 4.5.1. More info can be found at:
http://www.wwcfoa.ca
http://www.cfoa-acof.ca