For consistency (and to avoid E_STRICT warnings), public API functions should be declared as "static public". In many cases, it's simply "public" (or in some cases, implied).
Use of $this should be replaced with self::getInstance().
(In ) fixes #1122
(In ) fixes #1122 - per Matt's review
(In ) refs #1122 - fix usage
(In ) refs #1122 - fix core usage
(In ) refs #1122 - fix unit test
Tu summarize, instead of changing all API methods to being static, we decided to change all callers to not call methods statically as this could cause various issues in the future. Thanks vipsoft!