2.4 Principle 4 - Robust

Under the principle of robust [ http://www.w3.org/TR/2008/REC-WCAG20-20081211/#robust ], the guidelines state that content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies.

The W3C says:

Maximize compatibility with current and future user tools.

From: WCAG 2 at a Glance [ http://www.w3.org/WAI/WCAG20/glance/ ]