chore: add a comment about text nodes in .visible

Author: Marcy Sutton

lib/commons/text/visible.js

@@ -17,7 +17,7 @@ text.visible = function (element, screenReader, noRecursing) {
 	for (index = 0; index < length; index++) {
 		child = childNodes[index];
 
-		if (child.actualNode.nodeType === 3) {
+		if (child.actualNode.nodeType === 3) { // filter on text nodes
 			nodeValue = child.actualNode.nodeValue;
 			if (nodeValue && dom.isVisible(element.actualNode, screenReader)) {
 				result += nodeValue;