Clarify area definition for setViewport/setScissor

docs/api/renderers/WebGLRenderer.html

@@ -178,6 +178,8 @@
 
 		<h3>[method:null setScissor]( [page:Integer x], [page:Integer y], [page:Integer width], [page:Integer height] )</h3>
 		<div>Sets the scissor area from (x, y) to (x + width, y + height).</div>
+		
+		<div>NOTE: The point (x, y) is the lower left corner of the area to be set for both of these methods. The area is defined from left to right in width but bottom to top in height. The sense of the vertical definition is opposite to the fill direction of an HTML canvas element.</div>
 
 		<h3>[method:null enableScissorTest]( [page:Boolean enable] )</h3>
 		<div>Enable the scissor test. When this is enabled, only the pixels within the defined scissor area will be affected by further renderer actions.</div>