The update checker uses class_exists in several ways:
- As a guard clause around `class Whatever` definitions. This ensures we don't try to define a class that has already been loaded by a different plugin. In this case, autoloading is not necessary because we already know how to load the class. Also, we *want to* load our version of that class if possible - the version that gets loaded by somebody else's autoloader might be different and incompatible.
- As a guard clause before `require` statements that include a class. This is conceptually the same as the previous example.
- To enable optional features if Debug Bar is active. The latest compatible version of Debug Bar doesn't use autoloading, so it would again be unnecessary in this case.
Explanation:
WordPress includes a "quick edit" function that lets users edit certain post properties (title, categories, etc) from the "All Posts" list. WP calculates the width (colspan attribute) of the inline editor based on the number of <th>'s in the header of the first .widefat table on the page. When PUC and Debug Bar are both active, that first table happens to be the debug info table in our Debug Bar panel. This table does not have a <thead>. As a result, WordPress sets the colspan to zero, making the inline editor unusable.
Fixed by removing the "widefat" class from our debug info tables and adding a bunch of new CSS to emulate WordPress table style.
Yahnis Elsts