Media types

Media types
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7 Media types
Contents
7.1 Introduction to media types
7.2 Specifying media-dependent style sheets
7.2.1 The @media rule
7.3 Recognized media types
7.3.1 Media groups
(hide)
Note:
Several sections of this specification have been updated by other specifications. Please, see
"Cascading Style Sheets (CSS) — The Official Definition"
in the latest
CSS Snapshot
for a list of specifications and the sections they replace.
The CSS Working Group is also developing
CSS level 2 revision 2 (CSS 2.2).
7.1
Introduction to media types
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.
7.2
Specifying media-dependent style sheets
There are currently two ways to specify media dependencies for
style sheets:
Specify the target medium from a style sheet with the
@media
or
@import
at-rules.
Example(s):
@import url("fancyfonts.css") screen;
@media print {
/* style sheet for print goes here */
Specify the target medium within the document language. For
example, in HTML 4 (
[HTML4]
), the "media" attribute on the LINK
element specifies the target media of an external style sheet:




MEDIA="print, handheld" HREF="foo.css">

The body...


The
@import
rule is defined in
the
chapter on the cascade
7.2.1
The @media rule
An
@media
rule
specifies the target
media types
(separated
by commas) of a set of
statements
(delimited by curly
braces). Invalid statements must be ignored per
4.1.7 "Rule sets, declaration blocks,
and selectors"
and
4.2
"Rules for handling parsing errors."
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 }
Style rules outside of @media rules apply to all media types
that the style sheet applies to. At-rules inside @media are invalid in
CSS2.1.
7.3
Recognized media types
The names chosen for CSS media types reflect target devices for
which the relevant properties make sense. In the following list of CSS
media types the names of media types are normative, but the
descriptions are informative. Likewise, the "Media" field in the
description of each property is informative.
all
Suitable for all devices.
braille
Intended for braille tactile feedback devices.
embossed
Intended for paged braille printers.
handheld
Intended for handheld devices (typically small
screen, limited bandwidth).
Intended for paged material and for documents viewed on
screen in print preview mode. Please consult the section on
paged media
for information about formatting
issues that are specific to paged media.
projection
Intended for projected presentations, for example projectors.
Please consult the section on
paged media
for
information about formatting issues that are specific to paged media.
screen
Intended primarily for color computer screens.
speech
Intended for speech synthesizers. Note: CSS2 had a similar media type
called 'aural' for this purpose. See the appendix on
aural style sheets
for details.
tty
Intended for media using a fixed-pitch character grid (such as
teletypes, terminals, or portable devices with limited display
capabilities). Authors should not use
pixel units
with the "tty" media
type.
tv
Intended for television-type devices (low
resolution, color, limited-scrollability screens, sound available).
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 use different media types on different canvases. For
example, a document may (simultaneously) be shown in 'screen' mode on
one canvas and 'print' mode on another canvas.
Note that a multimodal media type is still only one media
type. The 'tv' media type, for example, is a multimodal media
type that renders both visually and aurally to a single canvas.
@media and @import rules with unknown media types (that are
nonetheless valid identifiers) are treated as if the unknown media
types are not present. If an @media/@import rule contains a malformed
media type (not an identifier) then the statement is invalid.
Note:
Media Queries supercedes this
error handling.
Example(s):
For example, in the following snippet, the rule on the P element applies
in 'screen' mode (even though the '3D' media type is not known).
@media screen, 3D {
P { color: green; }
Note.
Future updates of CSS may extend the list of media types. Authors
should not rely on media type names that are not yet defined
by a CSS specification.
7.3.1
Media groups
This section is informative, not normative.
Each CSS property definition specifies which media types the
property applies to. Since properties generally apply to several 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:
continuous
or
paged
visual
audio
speech
or
tactile
grid
(for
character grid devices), or
bitmap
interactive
(for
devices that allow user interaction), or
static
(for
those that do not).
all
(includes all media types)
The following table shows the relationships
between media groups and media types:
Relationship 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
embossed
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
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