Currently, `@since` is handled as a "simple taglet", (SimpleTaglet), meaning if a tag is present in a doc comment, it will be presented in the corresponding part of the output. No tag means nothing will appear in the output.

This works well for modules, packages, and top level classes. It also works well for "simple" members, like fields, constructors, and methods, because they are presented on the same page as their enclosing class, which will generally have its own `@since` tag and hence entry in the generated page.

It doesn't work for nested classes, because nested classes appear on a different page to that of the enclosing class. While an astute reader can click through to find the information on the enclosing class, it would be better if every page for every class had "Since:" info.