The presentation and textual content of a page must be able to be adapted to the dimensions of the browser window used by the user, without superimposing objects present or loss of information such as to render the content incomprehensible, including in the case of resizing, enlargement or reduction of the display area or characters in relation to the predefined values of these parameters.

WCAG 1.0 References: 3.4
Sec. 508 References: None