How could I execute my plugin just in frontend (not in backend)

Check the requested URI: if(!is_admin() && strpos($_SERVER[‘REQUEST_URI’], ‘wp-login.php’) === false && strpos($_SERVER[‘REQUEST_URI’], ‘wp-signup.php’) === false) { … } But it’s probably better to use a white-list style: if(is_front_page() || is_singular() || is_archive()) { … } These 3 tags should cover pretty much all of the front-end…

Where should I add the necessary code to add an extra attribute to the kses allowed tags array?

In detail there’s the constant CUSTOM_TAGS that allowes defining $allowedposttags, $allowedtags, $allowedentitynames. Then you can simply set CUSTOM_TAGS to true and define the globals in a function hooked before kses gets included. The first available hook to fire an action that defines $allowedposttags would be muplugins_loaded, but I don’t know if kses is loaded before … Read more

Can WordPress plugins “Talk to each other”?

Simple Answer would be yes. It really depends on the plugin. A good plugin will take use of the many API’s that WordPress has set up for development, such as the settings API. Most plugins will probably store their settings using get_option. A good place to start will be the WordPress Codex

Set a category for a page

Category is a taxonomy that applies to Posts. Pages are not Posts. Pages are Pages. If you need your content to use the Category taxonomy, you have a couple options: Use Posts, rather than Pages, for that content. Register the Category taxonomy for static Pages, e.g. by placing the following in functions.php (or in a … Read more