AMP_Blacklist_Sanitizer::strip_attributes_recursive PHP Method

    private function strip_attributes_recursive($node, $bad_attributes, $bad_protocols)
    {
        if ($node->nodeType !== XML_ELEMENT_NODE) {
            return;
        }
        $node_name = $node->nodeName;
        // Some nodes may contain valid content but are themselves invalid.
        // Remove the node but preserve the children.
        if ('font' === $node_name) {
            $this->replace_node_with_children($node, $bad_attributes, $bad_protocols);
            return;
        } elseif ('a' === $node_name && false === $this->validate_a_node($node)) {
            $this->replace_node_with_children($node, $bad_attributes, $bad_protocols);
            return;
        }
        if ($node->hasAttributes()) {
            $length = $node->attributes->length;
            for ($i = $length - 1; $i >= 0; $i--) {
                $attribute = $node->attributes->item($i);
                $attribute_name = strtolower($attribute->name);
                if (in_array($attribute_name, $bad_attributes)) {
                    $node->removeAttribute($attribute_name);
                    continue;
                }
                // on* attributes (like onclick) are a special case
                if (0 === stripos($attribute_name, 'on') && $attribute_name != 'on') {
                    $node->removeAttribute($attribute_name);
                    continue;
                } elseif ('a' === $node_name) {
                    $this->sanitize_a_attribute($node, $attribute);
                }
            }
        }
        $length = $node->childNodes->length;
        for ($i = $length - 1; $i >= 0; $i--) {
            $child_node = $node->childNodes->item($i);
            $this->strip_attributes_recursive($child_node, $bad_attributes, $bad_protocols);
        }
    }