Adding docs to external jars in eclipse

If you have some external jars, like in my case the GWT libraries and you want to add the handy javadoc to them - its not exactly obvious. You need to navigate on the Package explorer view to the "Referenced Libraries". Unfold this tree, and then right click on the relevant library. Click on properties and then javadoc. Add the directory and click validate just to check. Bingo - now the javadoc will appear using the tooltip in the main editor.