URI or URL?

There is a difference between a URI and a URL. A URL describes the location of the resource, the URI describes an id of the resource . A URI may be a location, a URL, or a name, a URN, of a resource.

In CSS Level 1, the url() functional notation was introduced to describe... URL, i.e. locations (a <url> CSS data type, though it wasn't explicitly defined that way).

In CSS Level 2, the same functional notation was extended to describe any URI, being a URL or URN. This led to the confusing fact that url() was used to create a <uri> CSS data type. Not only was this confusing, but URN are almost never used in the CSS usual case.

To fix this, CSS Level 3 came back to the initial definition, this time explicitly defined. The functional notation url() denotes a <url> CSS data type and no more the more generic <uri> CSS data type.

Remark that these semantic details doesn't change much for a web author, or the implementation details of the data type.

 <a_css_property>:  url("http://mysite.example.com/mycursor.png")

 <a_css_property>:  url(http://mysite.example.com/mycursor.png)

Note: Control characters above 0x7e are no longer allowed in unquoted url() notation starting in Firefox 15. See bug 752230 for more details.

.topbanner { background: url("topbanner.png") #00D no-repeat fixed; }

ul { list-style: square url(http://www.example.com/redball.png) }