The longdesc tag is implemented by placing a textual description of the image in a separate file. This allows you to describe the image in as much detail as you need. The alternative browser crowd recognizes a d link as an alternate to a longdesc tag. The two most used methods are inclusion of all dlinks included in a single file and the use of a different file for each dlink. All the descriptions are in one single file with different links.
All descriptions occupy their own separate files .