To add documentation to a model element, select the documentation tab in the Details pane. When you have imported Java source code, the javadoc contained in the source code is likewise imported and viewed in the documentation tab. When working with text based IDEs, you put your javadoc in doc comments (/** */). When using Poseidon's HTML editor, this is not necessary. The doc comments are added automatically to your source code when you generate it.
The UMLdoc Plug-In generates HTML documentation files, that look similar to Javadoc. But it includes your UML diagrams as jpeg images, and offers an improved navigation. Currently UMLdoc generates documentation for models, packages, classes, interfaces, operations, methods, associations, actors, use cases, extend and include relationships.
UMLdoc is also capable of generating external links. Any types from Java will be automatically linked to Sun's Java site, and other links can be created utilizing the @link tag. Additionally, any URL included in the documentation will be automatically detected and the link will be activated without requiring any other notation.