Using Actions and Filters in WordPress to Modify Plugins
У вашего броузера проблема в совместимости с HTML5
See how you can use the actions and filters that the plugins you install provide, to modify them so they work exactly how you need them to. This can be done by searching for do_action and apply_filters in a plugin file, then using the add_filter and add_action WordPress functions to hook into them without modifying the main plugin itself. https://pluginsforbeginners.com