Definition and Usage
The <url> CSS data type denotes a pointer to a resource. It has no proper syntax and can only be expressed through the url() functional notation.
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
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
To fix this, CSS Level 3 came back to the initial definition, this time explicitly defined. The functional notation
Remark that these semantic details doesn't change much for a web author, or the implementation details of the data type.
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.
Many CSS properties take a URL as value, such as background-image, cursor, @font-face, list-style etc.
The URI may be quoted by single or double quotes. Relative URIs are allowed and are relative to the URL of stylesheet (and not to the URL of the web page).
The url() functional notation
The URI may be quoted by single or double quotes. Relative URIs are allowed and are relative to the URL of stylesheet (and not to the URL of the web page).
Syntax
<a_css_property>: url("http://www.website.com/cursor.png") <a_css_property>: url(http://www.website.com/cursor.png)
Note: Control characters above 0x7e are no longer allowed in unquoted url() notation starting in Firefox 15.
Examples
.topbanner { background: url("topbanner.png") #00D no-repeat fixed; }
ul { list-style: square url(http://www.example.com/ball.png) }
Compatibility
Desktop browsers
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 1.0 | 1.0 (1.0) | 3.0 | 3.5 | 1.0 (85) |
Mobile browsers
Feature | Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|
Basic support | 1.0 | 1.0 (3.5) | yes | yes | 1.0 |