Referencing Documents: The URL
Creating Effective Links
Creating Searchable Documents
Establishing Document Relationships
Supporting Document Automation
Until this point, we've dealt with HTML documents as standalone entities, concentrating on the language elements you use for structure and to format your work. The true power of HTML, however, lies in its ability to join collections of documents together into a full library of information, and to link documents with other collections around the world. Just as readers have considerable control over how the document looks onscreen, with hyperlinks they also have control over the order of presentation as they navigate through your information. It's the "HT" in HTML--hypertext--and it's the twist that spins the Web.
A fundamental feature of hypertext is that you can hyperlink documents; you can point to another place inside the current document, inside another document in the local collection, or inside a document anywhere on the Internet. The documents thereby become an intricately woven web of information. Get the name analogy now? The target document is usually somehow related to and enriches the source; the linking element in the source should convey that relationship to the reader.
Hyperlinks can be used for all kinds of effects. They can be used inside tables of contents and lists of topics. With a click of the mouse on their browser screen, readers select and automatically jump to a topic of interest in the same document or to another document located in an entirely different collection somewhere around the world.
Hyperlinks also point readers to more information about a mentioned topic. "For more information, see `Kumquats on Parade,'" for example. HTML authors use hyperlinks to reduce repetitive information. For instance, we recommend you sign your name to each of your documents. Rather than include full contact information in each document, a hyperlink connects your name to a single place that contains your address, phone number, and so forth.
A hyperlink, or anchor in HTML standard parlance, is marked by the <a> tag and comes in two flavors. As we detail below, one type of anchor creates a hot spot in the document that, when activated and selected (usually with a mouse) by the user, causes the browser to link. It automatically loads and displays another portion of the same or another document altogether, or triggers some Internet service-related action, such as sending email or downloading a special file. The other type of anchor creates a label, a place in an HTML document that can be referenced as a hyperlink.
 Both types of HTML anchors use the same tag; perhaps that's why they have the same name. Nonetheless, we find it's easier if you differentiate them and think of the one type that provides the hotspot and address of a hyperlink as the "link," and the other type that marks the target portion of a document as the "anchor."