Indexes open up documents.
With a good index, readers can find information they need even if its location is not indicated by section headings or tables of contents. By using an index, a reader can go directly to a paragraph or sentence in one jump. An index created by people has some fundamental advantages over a computer-generated list. We index documents that you have already asked us to write or edit, and any document that you have written and would like us to index for you. Reference documents need indexes because they take readers into documents, giving them rapid access to information whose location is not indicated by section headings or tables of contents.