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 3 adds the ability to use `attr()` on **any** CSS property, and to use it for non-string values (e.g. numbers, colors).

  3. types: `attr()`

  4. types: `attr()`: <fallback>

  5. types: `attr()`: <type-or-unit>

  6. types: `attr()`: <type-or-unit>: <angle>

  7. types: `attr()`: <type-or-unit>: <color>

  8. types: `attr()`: <type-or-unit>: <frequency>

  9. types: `attr()`: <type-or-unit>: <integer>

  10. types: `attr()`: <type-or-unit>: <length>

  11. types: `attr()`: <type-or-unit>: <number>

  12. types: `attr()`: <type-or-unit>: <percentage>

  13. types: `attr()`: <type-or-unit>: <time>

  14. types: `attr()`: <type-or-unit>: <url>