Outlines allow interactive navigation of a document. An outline consists of a tree-structured hierarchy of outline items (also known as bookmarks), which serves as a visual table of contents that displays a document’s structure while allowing quick access to other parts of the document. By clicking the disclosure triangles left of parent outline items the items can be interactively opened or closed. Open items show their immediate children in the hierarchy, and each child in turn may be a parent of other children and may either be open or closed. Closed items hide all their descendants in the hierarchy. Clicking the text of a visible item performs its associated action. Usually this results in a jump to another part of the document, although it is possible to define external destinations to outline items.