In https://www.w3.org/TR/2016/CR-css-values-3-20160929/#references :

• [CSS-BACKGROUNDS-3] and [CSS3BG]
• [CSS-IMAGES-3] and [CSS3-IMAGES]
• [CSS-COLOR-3] and [CSS3COLOR]
• ([CSS-CASCADE-4] and [CSS3CASCADE])

These references are overlapping (or different version forms).