Best Practices for Style and Formatting of A-Z Browsable Website Indexes
The following are suggestions that apply specifically to website indexes. Where relevant, these guidelines may also apply to indexes posted on the web. Additional best practices for indexing in general are also applicable to all web indexes.
Site Navigation: The A-Z index should be clearly labeled and linked on the navigation menu of every page of the site. It can be called “Index,” “Site Index,” “A-Z Index,” “A-Z Site Index,” or “Topic Index,” and the index page itself should have the same title and heading.
Number of Pages: The index can be kept on one page or broken into multiple pages if it is long. If a majority of the letters of the alphabet require scrolling to view the letter section, then the index is long enough to consider breaking into individual letter pages.
Internal Index Navigation: Unless the index is so small that it can be viewed in its entirety on the screen with no scrolling, there should be a means of navigating the index either by hyperlinked “jump” letters of the alphabet at the top of each page or in a frame, or by having type-ahead scrolling enabled through an applet. The jump letters may be repeated at the bottom of the page, but usually a single top location suffices. “Back to top” (i.e., back to top of page) links should probably be added on pages that are lengthy and require scrolling.
Columns: Unless the index is so small that it can be viewed in its entirety on the screen with no scrolling, only a single column should be used, unlike the convention of dual-column printed indexes. Scrolling is easier when there is only a single column.
Entry Spacing: The entire index should be single-spaced to enable the browsing of more terms in a single screen view.
Entry Case: Lower-case should be used for entry topics to better distinguish them from page titles and other proper nouns.
Entry Font Color: If some index entries are not to be hyperlinked (such as main entries that have linked subentries), then a different color and perhaps also underlining should be used for the hyperlinked entries to indicate that they are links. A different visited-link color should also be used to indicate when an entry or its equivalent (double-posted variant) has been clicked on in order to visit a page.
Entry Font Size: A standard font size should be used, that is no smaller than that used in the website’s content text, so that it is easy to read. This is unlike book indexes which tend to use one-point smaller for index fonts.
Entry Length: Although the single column format supports long entries, conciseness is still important to enable quick browsing. Long entries are best left to proper nouns.
Entries to Nonstandard Pages: A convention (different color, parenthetical notes, added small graphic icon, etc.) should be used to indicate links to nonstandard pages, such as external links, password restricted pages, and non-HTML pages such as PDFs or Word documents.
Indenting: Indenting of subentries is the preferred style, with hanging indents for each subentry to allow quick browsing.
Subentry Levels: Up to three levels is acceptable. More than three is problematic, since only part of the index is visible in the screen view. A tendency to four levels indicates that a hierarchical taxonomy would be a better option than an A-Z index for the organization of topics.
Number of Subentries: Contrary to book-indexing style, single subentries are acceptable, since multiple locators are usually not indicated for a single entry in a web index. The number of subentries should best not exceed a screen view.
Cross-references: If a See or See also reference points to an index entry that has no subentries, then the link should be to the source page and not the other referred term in the index, to eliminate the need for an extra click within the index. If there are subentries under the referred term, then the See or See also reference should link to the preferred term within the index.