WP-Mix

Two little interesting tidbits about WordPress: must-use (mu) plugins and drop-ins. Do you know them?

Must use plugins

Must-use or “mu” plugins are plugins that are loaded automatically regardless of how anything else is configured. They don’t even need the usual plugin headers, just PHP works fine. mu plugins must be placed in the directory: /wp-content/mu-plugins/. Note that two constants are available: WPMU_PLUGIN_DIR and WPMU_PLUGIN_URL.

Drop Ins

The other interesting thing about WordPress is the “drop in”. Drop-ins are used to add or replace default WordPress functionality. So for example, if a file named db.php exists in the /wp-content/ directory, it will be processed as a custom database class. All drop-in files are placed in the wp-content directory by default. To use a different directory you may specify it using the WP_CONTENT_DIR variable.

Drop-ins are a scattered lot of useful scripts for a variety of tasks:

Source: Data taken from global function _get_dropins() in wp-admin/includes/plugin.php. Table data grabbed from here.

Related

• WordPress db-error.php drop-in template