jEdit 4.2 used to run plugins that were designed only for the 4.1 plugin API, but plugins that are missing the "activate" property will no longer load properly in 4.3.
There are two new properties that all plugins can have:
description
and
longdescription
. The former is just a string
property, while the latter is a reference to an html or text file.
See EditPlugin API docs for details.