The issue stems from how Flash is referenced within a web page. Traditionally Flash was detected by HTML using either <embed> or <object> tags, however both tags have accessibility and plug-in detection issues, and <embed> is invalid XHTML. These methods can cause some browsers and screen readers to misinterpret or entirely ignore your Flash content.

My favorite solution to this problem has been Bobby van der Sluis’ Unobtrusive Flash Object (UFO), but it was recently deprecated and replaced by Geoff Stearns’ SWFObject 2.0. Like UFO, SWFObject is a DOM script that detects the Flash plug-in and embeds Flash objects. It’s JavaScript API provides an amazing and complete toolset for embedding SWF files and retrieving Flash Player-related information. It has its roots in the web standards community and is designed to support W3C standards-compliant, accessible and search engine friendly web design. The handy JavaScript detection determines whether Flash content or alternative content should be shown and avoids outdated Flash plug-ins break Flash content. The example below illustrates how simple it is to detecting Flash and add alternative content.