How to inject markup in the head tag as early as possible in Wordpress Plugin

If you are a Wordpress Plugin developer, you'd already know that to add markup in the head of the HTML page you can use the following hook:

add_action('wp_head', 'add_head_markup');

Working on a Wordpress Plugin about open-graph tags I had the need to write those tags as early as possible in the HTML page because other tags, made from other plugins, might override them.

Today I've learned that adding a third parameter, it instructs Wordpress a specific order of injection.

Adding the lowest possible number, 1 you can put the markup at the beginning of the head tag:

add_action('wp_head', 'add_head_markup', 1);

Of course, if other plugins, or Wordpress itself, use the same number, I don't really know which will be the order of injection, I guess based on alphabetical order of the loaded plugins/functions.

There's no mention of it in the official documentation, though.