The Message class constructor has long supported passing an array of
keys for fallback messages, and wfMessage passes the $keys parameter
through unchanged.
And since this is already in use in core, we may as well document it.
Change-Id: I8f7f9ade87e855300650b2e7e31b9303daa96ac5
*
* This function replaces all old wfMsg* functions.
*
- * @param string $key Message key
+ * @param string|string[] $key Message key, or array of keys
* @param mixed $params,... Normal message parameters
* @return Message
*