adds comment explaining why canvas_x/y might be null
adds comment explaining why canvas_x/y might be null

ProjectSidewalk/SidewalkWebpage,ProjectSidewalk/SidewalkWebpage,ProjectSidewalk/SidewalkWebpage,ProjectSidewalk/SidewalkWebpage,ProjectSidewalk/SidewalkWebpage,ProjectSidewalk/SidewalkWebpage