1. CSS Generated content for pseudo-elements

   Method of displaying text or images before or after the given element's contents using the ::before and ::after pseudo-elements. All browsers with support also support the `attr()` notation in the `content` property.

2. CSS3 attr() function for all properties

   While `attr()` is supported for effectively all browsers for the `content` property, CSS Values and Units Level 5 adds the ability to use `attr()` on **any** CSS property, and to use it for non-string values (e.g. numbers, colors).