The individual package index files (i.e., Package-<package-name>.html) would be more useful if each Interface, Class, Exception, and Error listed were augmented with a brief summary of that entity.  This is analogous to the one-line summary information that appears for the Field, Constructor, and Method Indexes at the top of each class file (i.e., <package-name>.<class-name>.html).  By convention, the summary could be the first sentence from the entity's top-level doc comment, following the analogy.