An item, often but not always a paragraph, makes up one self-contained element of a wiki page's story.
Items can be made of words, numbers, images, formulas, sounds and diagrams. They do things, creating and responding to events.
An item may be expressed as markup that can be edited by double-clicking the item. Some markups format words, others program actions.
Type cmd/alt-i in an editor to read about an item's markup.