Simple outliners only contain content that is explicitly entered or imported into the document. More advanced outliners can link to external sources. Simple links are usually URL-like text or badges that when clicked open a file or Web page. More advanced implementations import or display the contents of the referenced source.

By far, the most amazing of our applications in this regard is Tinderbox, shown in the screenshot. A note can be fetched, displayed and filtered from a Web page, or a dynamic RSS feed. (Real Simple Syndication is a common Web news and blog publishing standard.) Or the note can find anything that can be AppleScripted because opening a note can trigger a script. Tinderbox also supports the weaker version of link references to files or URLs. Inspiration and NoteBook do this too. Hog Bay Notebook is limited to URLs. Radio can only import other Radio outlines.