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One of the most important features of style sheets is that they specify how a document is to be presented on different media: on the screen, on paper, with a speech synthesizer, with a braille device, etc.
Certain CSS properties are only designed for certain media (e.g., the 'page-break-before' property only applies to paged media). On occasion, however, style sheets for different media types may share a property, but require different values for that property. For example, the 'font-size' property is useful both for screen and print media. The two media types are different enough to require different values for the common property; a document will typically need a larger font on a computer screen than on paper. Therefore, it is necessary to express that a style sheet, or a section of a style sheet, applies to certain media types.
There are currently two ways to specify media dependencies for style sheets:
@import url("fancyfonts.css") screen; @media print { /* style sheet for print goes here */ }
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> <HTML> <HEAD> <TITLE>Link to a target medium</TITLE> <LINK REL="stylesheet" TYPE="text/css" MEDIA="print, handheld" HREF="foo.css"> </HEAD> <BODY> <P>The body... </BODY> </HTML>
The @import rule is defined in the chapter on the cascade.
An @media rule specifies the target media types (separated by commas) of a set of rules (delimited by curly braces). The @media construct allows style sheet rules for various media in the same style sheet:
@media print { body { font-size: 10pt } } @media screen { body { font-size: 13px } } @media screen, print { body { line-height: 1.2 } }
The names chosen for CSS media types reflect target devices for
which the relevant properties make sense. The names of media types are normative.In the following list of CSS
media types,types the names of media types are normative, but the
parentheticaldescriptions are not normative.informative. Likewise, the "Media" field in the
description of each property is informative.
Media type names are case-insensitive.
Media types are mutually exclusive in the sense that a user agent can only support one media type when rendering a document. However, user agents may have different modes which support different media types.
Unknown media type names should not result in the @media rule being ignored.
Note.
Future versions of CSS may extend this list.the list of media types. Authors
should not rely on media type names that are not yet defined
by a CSS specification.
This section is informative, not normative.
Each CSS property definition specifies thewhich media types for whichthe
property must be implemented by a conforming user agent .applies to. Since properties generally apply to several media,media
types, the "Applies to media" section of each property definition
lists media groups
rather than individual media types. Each property applies to all media
types in the media groups listed in its definition.
CSS 2.1 defines the following media groups:
The following table shows the relationships between media groups and media types:
Media Types | Media Groups | |||
---|---|---|---|---|
continuous/paged | visual/audio/speech/tactile | grid/bitmap | interactive/static | |
braille | continuous | tactile | grid | both |
| paged | tactile | grid | static |
handheld | both | visual, audio, speech | both | both |
paged | visual | bitmap | static | |
projection | paged | visual | bitmap | interactive |
screen | continuous | visual, audio | bitmap | both |
speech | continuous | speech | N/A | both |
tty | continuous | visual | grid | both |
tv | both | visual, audio | bitmap | both |