Read the value of a class constant.

This is the same as just typing self::CONSTANTNAME, but throws a more useful message if the constant is not defined and allows the constant to be limited to a maximum length.

Should this panel pull content in over AJAX?

Normally, panels use AJAX to render their content. This makes the page interactable sooner, allows panels to render in parallel, and prevents one slow panel from slowing everything down.

However, some panels are very cheap to build (i.e., no expensive service calls or complicated rendering). In these cases overall performance can be improved by disabling async rendering so the panel rendering happens in the same process.