add allow attributes to parse

Author: ryanlntn

vendor/assets/javascripts/wysihtml5.js

@@ -4899,6 +4899,7 @@ wysihtml5.dom.parse = (function() {
     var attributes          = {},                         // fresh new set of attributes to set on newNode
         setClass            = rule.set_class,             // classes to set
         addClass            = rule.add_class,             // add classes based on existing attributes
+        allowAttributes     = rule.allow_attributes,      // copy attributes from old to new node
         setAttributes       = rule.set_attributes,        // attributes to set on the current node
         checkAttributes     = rule.check_attributes,      // check/convert values of attributes
         allowedClasses      = currentRules.classes,
@@ -4918,6 +4919,17 @@ wysihtml5.dom.parse = (function() {
     if (setAttributes) {
       attributes = wysihtml5.lang.object(setAttributes).clone();
     }
+
+    if (allowAttributes) {
+      allowAttributesLength = allowAttributes.length;
+      for (i = 0; i<allowAttributesLength; i++) {
+        attributeName = allowAttributes[i];
+        newAttributeValue = _getAttribute(oldNode, attributeName);
+        if (typeof(newAttributeValue) === "string") {
+          attributes[attributeName] = newAttributeValue;
+        }
+      }
+    }
 
     if (checkAttributes) {
       for (attributeName in checkAttributes) {