WebGLBackground: Update comment. (#24474)

src/renderers/webgl/WebGLBackground.js

@@ -86,7 +86,7 @@ function WebGLBackground( renderer, cubemaps, state, objects, alpha, premultipli
 
 				};
 
-				// enable code injection for non-built-in material
+				// add "envMap" material property so the renderer can evaluate it like for built-in materials
 				Object.defineProperty( boxMesh.material, 'envMap', {
 
 					get: function () {
@@ -141,7 +141,7 @@ function WebGLBackground( renderer, cubemaps, state, objects, alpha, premultipli
 
 				planeMesh.geometry.deleteAttribute( 'normal' );
 
-				// enable code injection for non-built-in material
+				// add "map" material property so the renderer can evaluate it like for built-in materials
 				Object.defineProperty( planeMesh.material, 'map', {
 
 					get: function () {