framework/helpers/BaseFileHelper.php
protected static function loadMimeTypes($magicFile)
    {
        if ($magicFile === null) {
            $magicFile = static::$mimeMagicFile;
        }
        $magicFile = Yii::getAlias($magicFile);
        if (!isset(self::$_mimeTypes[$magicFile])) {
            self::$_mimeTypes[$magicFile] = require $magicFile;
        }

        return self::$_mimeTypes[$magicFile];
    }
protected static function loadMimeTypes($magicFile)
    {
        if ($magicFile === null) {
            $magicFile = static::$mimeMagicFile;
        }
        $magicFile = Yii::getAlias($magicFile);
        if (!isset(self::$_mimeTypes[$magicFile])) {
            self::$_mimeTypes[$magicFile] = require $magicFile;
        }

        return self::$_mimeTypes[$magicFile];
    }
Loads MIME types from the specified file.
@param string $magicFile the path (or alias) of the file that contains all available MIME type information.
If this is not set, the file specified by [[mimeMagicFile]] will be used.
@return array the mapping from file extensions to MIME types