Plain Language Recommendations
Decoration, formatting, and invisible elements: If non-text content is pure decoration, is used only for visual formatting, or is not presented to users, then it must be implemented in a way that it can be ignored by assistive technology [null alt text (alt=“”) or implemented as CSS decorative background.]
WCAG 2.0 Recommendations
Guideline 1.1: Text Alternatives
Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.