Description Available in a Separate Document Provides Efficiency

Powerful Technique

One external file provides and controls the description for multiple docs

Using one global document to provide descriptions for multiple instances of the same image is a powerful, portable, re-usable, technique. It provides efficiency and scalability making authoring and maintenance easy wherever instances of the same image are used in multiple locations. It is analogous to the power of external style sheets.

The technique saves time and money by:

Global long descriptions can be applied across multiple sites, or across an entire site, or across a subset of pages, and doing so means that you only need to update one file if you need to make a change.

As documented by the use cases and evidenced by real world examples a description available in a separate document provides easy reuse of the targeted description from multiple sources (i.e. ability for an image to appear in multiple documents throughout a site or throughout multiple sites or from an HTML email while at the same time linking to one longdesc document).

Other "solutions" such as figcaption, details, and aria-describedby as implemented lack this functionality. They are hamstrung to on-page descriptions.

Examples in the Wild

The CSS Squirrel, SEO Design, the Lambda Theta Phi Latin Fraternity, the Texas State Library , and the University of Minnesota Duluth use images in separate documents that share the same long description page. This technique is key to the logo description use cases and the lightbox description use case as evidenced through examples in the wild, Geoff Freed has indicated that professional content producers (such as those involved in the ePub initiative, and the US federally-funded DIAGRAM Project) are interested and ready to use longdesc to externally store descriptions to facilitate etext descriptions and describe etext Images.

Of long description techniques, using a separate document is a prevalent design pattern/cowpath with authors who supply descriptions. Less than two-dozen on-page long descriptions via anchor were found out of over two thousand examples in the wild.

Code and User Interface Pattern

The code and UI patterns for how to navigate to an external page with longdesc are well established (and used for example by JAWS and Opera).