We propose implicit hyperlinks that use indices to solve the problems with HTML's explicit hyperlinks. The basic idea is that an index associates attributes with text phrases. The browser implements the policy behind the mechanism, i.e. what action should be taken based upon the user's actions and the attributes associated with the text. Indices are not restricted in the attributes they contain, however. It is up to the browser to decide what it does with a particular attribute, if anything.
Indices also share properties with symbol tables for statically scoped programming languages.
Finally, indices have some similarities to search engines. In its simplest form, an index is a collection of phrases and associated attributes. The simple format of the index and the clean separation of mechanism and policy allows for much more complex browser behavior than is possible using HTML hyperlinks. For example, our prototype browser displays the definition of an entry when the cursor is placed over text matching the phrase. The description makes it easier for the reader to decide if the suggested URL is worth viewing.