An SVG document fragment can range from an empty fragment (i.e.,
no content inside of the 'svg' element), to a very simple SVG
document fragment containing a single SVG graphics element
such as a 'rect', to a complex, deeply nested collection of
container elements and graphics elements.
An SVG document fragment can stand by itself as a self-contained
file or resource, in which case the SVG document fragment is an SVG
document, or it can be embedded inline as a fragment within a parent
XML document.
The following example shows simple SVG
content embedded inline as a fragment within a parent XML document.
Note the use of XML namespaces to indicate that the 'svg' and
'ellipse' elements belong to the SVG namespace:
]]>
This example shows a slightly more complex (i.e., it contains
multiple rectangles) stand-alone, self-contained SVG document:
'svg' elements can appear in the middle of SVG content. This
is the mechanism by which SVG document fragments can be embedded within
other SVG document fragments.
Another use for 'svg' elements within the middle
of SVG content is to establish a new viewport. (See
Establishing a new
viewport.)
In all cases, for compliance with the
Namespaces in XML Recommendation
[XML-NS], an SVG namespace
declaration must be provided so that all SVG elements are identified
as belonging to the SVG namespace. The following are possible ways to
provide a namespace declaration. An 'xmlns'
attribute without a namespace prefix could be specified on an
'svg' element, which means that SVG is the default namespace
for all elements within the scope of the element with the 'xmlns' attribute:
]]>
If a namespace prefix is specified on the 'xmlns'
attribute (e.g., xmlns:svg="http://www.w3.org/2000/svg"),
then the corresponding namespace is not the default namespace, so an
explicit namespace prefix must be assigned to the elements:
]]>
Namespace prefixes can be specified on ancestor elements (illustrated
in the above example). For more
information, refer to the Namespaces in XML Recommendation
[XML-NS].
Indicates the SVG language version to which this
document fragment conforms.
In SVG 1.0 [SVG10],
this attribute was fixed to the value '1.0'.
For SVG 1.1, the attribute should have the value
'1.1'. Animatable:
no.
baseProfile = profile-name
Describes the minimum SVG language profile that the
author believes is necessary to correctly render the
content. The attribute does not specify any processing
restrictions; It can be considered metadata. For example,
the value of the attribute could be used by an authoring
tool to warn the user when they are modifying the document
beyond the scope of the specified base profile. Each SVG
profile should define the text that is appropriate for this
attribute.
If the attribute is not specified, the effect is as if a
value of 'none' were specified. Animatable:
no.
(Has no meaning or effect on outermost svg
elements.)
The x-axis coordinate of one corner of the rectangular
region into which an embedded 'svg' element is placed.
If the attribute is not specified, the effect is as if a
value of '0' were specified. Animatable:
yes.
(Has no meaning or effect on outermost svg
elements.)
The y-axis coordinate of one corner of the rectangular
region into which an embedded 'svg' element is placed.
If the attribute is not specified, the effect is as if a
value of '0' were specified. Animatable:
yes.
For outermost svg elements,
the intrinsic width of the SVG document fragment.
For embedded 'svg'
elements, the width of the rectangular region into which
the 'svg' element is
placed.
A negative value is an error (see Error processing).
A value of zero disables rendering of the element.
If the attribute is not specified, the effect is as if a
value of '100%' were specified. Animatable:
yes.
For outermost svg elements,
the intrinsic height of the SVG document
fragment. For embedded 'svg' elements, the height of
the rectangular region into which the 'svg' element is placed.
A negative value is an error (see Error processing).
A value of zero disables rendering of the element.
If the attribute is not specified, the effect is as if a
value of '100%' were specified. Animatable:
yes.
If an SVG document is likely to be referenced as a component
of another document, the author will often want to include a
'viewBox' attribute on the outermost svg element of the
referenced document. This attribute provides a convenient way to design
SVG documents to scale-to-fit into an arbitrary viewport.
Grouping constructs, when used in conjunction with the 'desc'
and 'title' elements, provide information about document
structure and semantics. Documents that are rich in structure may be
rendered graphically, as speech, or as braille, and thus promote
accessibility.
A group of elements, as well as individual objects, can be given
a name using the 'id' attribute. Named groups are needed for
several purposes such as animation and re-usable objects.
An example:
A 'g' element can contain other 'g' elements nested
within it, to an arbitrary depth. Thus, the following is possible:
]]>
Any element that is not contained within a 'g' is treated (at
least conceptually) as if it were in its own group.
The 'g' element
Defining content for reuse, and the 'defs' element
Overview
SVG allows graphical objects to be defined for later reuse.
To do this, it makes extensive use of IRI references
[RFC3987] to these other objects.
For example, to fill a rectangle with a linear gradient, you first
define a 'linearGradient' element and give it an ID, as in:
...
]]>
You then reference the linear gradient as the value of the
'fill' property for the rectangle, as in:
]]>
Some types of element, such as gradients, will not by themselves produce a graphical result. They can therefore be placed anywhere convenient. However, sometimes it is desired to define a graphical object and prevent it from being directly rendered. it is only there to be referenced elsewhere. To do this, and to allow convenient grouping defined content, SVG provides the 'defs' element.
The 'defs' element is a container element for
referenced elements. For understandability and
accessibility reasons, it is recommended
that, whenever possible, referenced elements be defined inside
of a 'defs'.
The content model for 'defs' is the same as for the
'g' element; thus, any element that can be a child of a
'g' can also be a child of a 'defs', and vice versa.
Elements that are descendants of a 'defs' are not rendered directly;
they are prevented from becoming part of the rendering tree
just as if the 'defs' element were a 'g' element and the
'display' property were set to none.
Note, however, that the descendants of a 'defs' are
always present in the source tree and thus can always be
referenced by other elements; thus, the value of the 'display'
property on the 'defs' element or any of its descendants does not
prevent those elements from being referenced by other elements.
To provide some SVG user agents with an opportunity to
implement efficient implementations in streaming environments,
creators of SVG content are encouraged to place all elements
which are targets of local IRI references within a 'defs'
element which is a direct child of one of the ancestors of the
referencing element. For example:
In the document above, the linear gradient is defined within
a 'defs' element which is the direct child of the 'svg'
element, which in turn is an ancestor of the 'rect' element which
references the linear gradient. Thus, the above document conforms to the
guideline.
The 'desc'
and 'title' elements
Each container element or graphics element in an SVG drawing
can supply a 'desc' and/or a 'title' description string where
the description is text-only. When the current SVG document fragment is
rendered as SVG on visual media, 'desc' and 'title' elements are
not rendered as part of the graphics. User agents may, however, for example,
display the 'title' element as a tooltip, as the pointing device moves
over particular elements. Alternate presentations are possible, both visual and
aural, which display the 'desc' and 'title' elements but do not
display 'path' elements or other graphics elements. This is
readily achieved by using a different (perhaps user) style sheet. For deep
hierarchies, and for following 'use' element references, it is
sometimes desirable to allow the user to control how deep they drill down into
descriptive text.
In conforming SVG document fragments, any 'title' element should be
the first child element of its parent. Note that those implementations that do
use 'title' to display a tooltip often will only do so if the
'title' is indeed the first child element of its parent.
The following is an example. In typical operation, the SVG user agent would
not render the 'desc' and 'title' elements but would render the
remaining contents of the 'g' element.
]]>
Description and title elements can contain marked-up text
from other namespaces. Here is an example:
]]>
Authors should always provide a 'title' child element to the
outermost svg element within a stand-alone SVG document. The
'title' child element to an 'svg' element serves the
purposes of identifying the content of the given SVG document
fragment. Since users often consult documents out of context,
authors should provide context-rich titles. Thus, instead of a
title such as "Introduction", which doesn't provide much
contextual background, authors should supply a title such as
"Introduction to Medieval Bee-Keeping" instead. For reasons of
accessibility, user agents should always make the content of
the 'title' child element to the outermost svg element
available to users. The mechanism for doing so depends on the user agent
(e.g., as a caption, spoken).
The DTD definitions of many of SVG's elements (particularly,
container and text elements) place no restriction on the
placement or number of the 'desc' and 'title' sub-elements.
This flexibility is only present so that there will be a consistent
content model for container elements, because some container
elements in SVG allow for mixed content, and because
the mixed content rules for XML
([XML10], section 3.2.2)
do not permit the desired restrictions. Representations of
future versions of the SVG language might use more expressive
representations than DTDs which allow for more restrictive
mixed content rules. It is strongly recommended that at most
one 'desc' and at most one 'title' element appear as a
child of any particular element, and that these elements appear
before any other child elements (except possibly
'metadata' elements) or character data content. If user agents need to
choose among multiple 'desc' or 'title' elements for processing
(e.g., to decide which string to use for a tooltip), the user
agent shall choose the first one.
The 'symbol' element
The 'symbol' element is used to define graphical template objects
which can be instantiated by a 'use' element.
The use of 'symbol' elements for graphics that are used multiple
times in the same document adds structure and semantics. Documents that are rich
in structure may be rendered graphically, as speech, or as
braille, and thus promote accessibility.
The key distinctions between a 'symbol' and a 'g' are:
A 'symbol' element itself is not rendered. Only instances of a
'symbol' element (i.e., a reference to a 'symbol' by
a 'use' element) are rendered.
'symbol' elements are never rendered directly; their only usage is
as something that can be referenced using the
'use' element. The 'display' property does not apply
to the 'symbol' element; thus, 'symbol' elements are
not directly rendered even if the 'display' property is set to a
value other than none, and 'symbol'
elements are available for referencing even when the
'display' property on the 'symbol' element or any of its
ancestors is set to none.
The 'use' element
Any 'svg', 'symbol', 'g', graphics element or
other 'use' is potentially a
template object that can be re-used (i.e., "instanced") in the
SVG document via a 'use'
element. The 'use' element
references another element and indicates that the graphical
contents of that element is included/drawn at that given point
in the document.
Unlike 'image', the 'use' element cannot reference
entire files.
The 'use' element has
optional attributes 'use/x', 'use/y', 'use/width' and 'use/height' which are used to map the
graphical contents of the referenced element onto a rectangular
region within the current coordinate system.
The effect of a 'use'
element is as if the contents of the referenced element were
deeply cloned into a separate non-exposed DOM tree which had
the 'use' element as its
parent and all of the 'use'
element's ancestors as its higher-level ancestors. Because the
cloned DOM tree is non-exposed, the SVG Document Object Model
(DOM) only contains the 'use'
element and its attributes. The SVG DOM does not show the
referenced element's contents as children of 'use' element.
For user agents that support Styling with CSS, the
conceptual deep cloning of the referenced element into a
non-exposed DOM tree also copies any property values resulting
from the CSS cascade
([CSS2], chapter 6)
on the referenced element and its contents. CSS2 selectors can
be applied to the original (i.e., referenced) elements because
they are part of the formal document structure. CSS2 selectors
cannot be applied to the (conceptually) cloned DOM tree because
its contents are not part of the formal document structure.
Property inheritance, however, works as if the referenced
element had been textually included as a deeply cloned child of
the 'use' element. The
referenced element inherits properties from the 'use' element and the 'use' element's ancestors. An
instance of a referenced element does not inherit properties
from the referenced element's original parents.
If event attributes are assigned to referenced elements,
then the actual target for the event will be the
SVGElementInstance object
within the "instance tree" corresponding to the given
referenced element.
The event handling for the non-exposed tree works as if the
referenced element had been textually included as a deeply
cloned child of the 'use'
element, except that events are dispatched to the SVGElementInstance objects. The
event's target and currentTarget attributes are set to the
SVGElementInstance that
corresponds to the target and current target elements in the
referenced subtree. An event propagates through the exposed and
non-exposed portions of the tree in the same manner as it would
in the regular document tree: first going from the root element
to the 'use' element and then
through non-exposed tree elements in the capture phase,
followed by the target phase at the target of the event, then
bubbling back through non-exposed tree to the use element and
then back through regular tree to the root element in bubbling
phase.
An element and all its corresponding SVGElementInstance objects
share an event listener list. The currentTarget attribute of
the event can be used to determine through which object an
event listener was invoked.
The behavior of the 'visibility' property conforms to
this model of property inheritance. Thus, specifying 'visibility:hidden' on a 'use' element does not guarantee
that the referenced content will not be rendered. If the 'use' element specifies 'visibility:hidden' and the element
it references specifies 'visibility:hidden' or 'visibility:inherit', then that one
element will be hidden. However, if the referenced element
instead specifies 'visibility:visible', then that
element will be visible even if the 'use' element specifies 'visibility:hidden'.
Animations on a referenced element will cause the instances
to also be animated.
A 'use' element has the
same visual effect as if the 'use' element were replaced by the
following generated content:
In the generated content, the 'use' will be replaced by 'g', where all attributes
from the 'use' element
except for 'use/x', 'use/y', 'use/width', 'use/height' and 'use/xlink:href' are transferred to
the generated 'g' element. An additional
transformation translate(x,y)
is appended to the end (i.e., right-side) of the 'transform' attribute on the
generated 'g', where x and y represent the values of the 'use/x' and 'use/y' attributes on the 'use' element. The referenced 'symbol' and its contents are
deep-cloned into the generated tree, with the exception that
the 'symbol' is replaced by an 'svg'. This generated 'svg' will always have
explicit values for attributes 'svg/width' and 'svg/height'. If attributes 'use/width' and/or 'use/height' are provided on the 'use' element, then these
attributes will be transferred to the generated 'svg'. If attributes 'use/width' and/or 'use/height' are not specified, the
generated 'svg' element will use values
of '100%' for these attributes.
In the generated content, the 'use' will be replaced by 'g', where all attributes
from the 'use' element
except for 'use/x', 'use/y', 'use/width', 'use/height' and 'use/xlink:href' are transferred to
the generated 'g' element. An additional
transformation translate(x,y)
is appended to the end (i.e., right-side) of the 'transform' attribute on the
generated 'g', where x and y represent the values of the 'use/x' and 'use/y' attributes on the 'use' element. The referenced 'svg' and its contents are
deep-cloned into the generated tree. If attributes 'use/width' and/or 'use/height' are provided on the 'use' element, then these values
will override the corresponding attributes on the 'svg' in the generated
tree.
Otherwise:
In the generated content, the 'use' will be replaced by 'g', where all attributes
from the 'use' element
except for 'use/x', 'use/y', 'use/width', 'use/height' and 'use/xlink:href' are transferred to
the generated 'g' element. An additional
transformation translate(x,y)
is appended to the end (i.e., right-side) of the 'transform' attribute on the
generated 'g', where x and y represent the values of the 'use/x' and 'use/y' attributes on the 'use' element. The referenced
object and its contents are deep-cloned into the generated
tree.
For user agents that support Styling with CSS, the
generated 'g' element carries along with
it the "cascaded" property values on the 'use' element which result from
the CSS cascade
([CSS2], chapter 6).
Additionally, the copy (deep clone) of the referenced resource
carries along with it the "cascaded" property values resulting
from the CSS cascade on the original (i.e., referenced)
elements. Thus, the result of various CSS selectors in
combination with the 'class' and 'style attribute' attributes are, in effect,
replaced by the functional equivalent of a 'style attribute' attribute in the generated
content which conveys the "cascaded" property values.
Example Use01 below has a
simple 'use' on a 'rect'.
The visual effect would be equivalent to the following document:
The visual effect would be equivalent to the following document:
Example Use03 illustrates
what happens when a 'use' has
a 'transform' attribute.
The visual effect would be equivalent to the following document:
Example Use04 illustrates a
'use' element with various
methods of applying CSS styling.
The visual effect would be equivalent to the following
document. Observe that some of the style rules above apply to
the generated content (i.e., rules 1-6, 10-12), whereas others
do not (i.e., rules 7-9). The rules which do not affect the
generated content are:
Rules 7 and 8: CSS selectors only apply to the formal
document tree, not on the generated tree; thus, these
selectors will not yield a match.
Rule 9: The generated tree only inherits from the
ancestors of the 'use'
element and does not inherit from the ancestors of the
referenced element; thus, this rule does not affect the
generated content.
In the generated content below, the selectors that yield a
match have been transferred into inline 'style attribute' attributes for
illustrative purposes.
When a 'use' references
another element which is another 'use' or whose content contains a
'use' element, then the deep
cloning approach described above is recursive. However, a set
of references that directly or indirectly reference a element
to create a circular dependency is an error, as described in References and the 'defs' element.
The x-axis coordinate of one corner of the rectangular
region into which the referenced element is placed.
If the attribute is not specified, the effect is as if a
value of "0" were specified. Animatable:
yes.
The y-axis coordinate of one corner of the rectangular
region into which the referenced element is placed.
If the attribute is not specified, the effect is as if a
value of "0" were specified. Animatable:
yes.
The width of the rectangular region into which the
referenced element is placed. A negative value is an error
(see Error
processing). A value of zero disables rendering of this
element. Animatable:
yes.
The height of the rectangular region into which the
referenced element is placed. A negative value is an error
(see Error
processing). A value of zero disables rendering of this
element. Animatable:
yes.
The 'image' element
indicates that the contents of a complete file are to be
rendered into a given rectangle within the current user
coordinate system. The 'image' element can refer to raster
image files such as PNG or JPEG or to files with MIME type of
"image/svg+xml". Conforming SVG
viewers need to support at least PNG, JPEG and SVG format
files.
The result of processing an 'image' is always a four-channel
RGBA result. When an 'image'
element references a raster image file such as PNG or JPEG
files which only has three channels (RGB), then the effect is
as if the object were converted into a 4-channel RGBA image
with the alpha channel uniformly set to 1. For a single-channel
raster image, the effect is as if the object were converted
into a 4-channel RGBA image, where the single channel from the
referenced object is used to compute the three color channels
and the alpha channel is uniformly set to 1.
An 'image' element
establishes a new viewport for the referenced file as described
in Establishing
a new viewport. The bounds for the new viewport are
defined by attributes 'x', 'y', 'width' and 'height'. The placement and scaling
of the referenced image are controlled by the 'preserveAspectRatio' attribute on
the 'image' element.
When an 'image' element
references an SVG image, the 'clip' and 'overflow' properties on the root element in
the referenced SVG image are ignored (in the same manner as the
'x', 'y', 'width' and 'height' attributes are ignored). Unless the value of
'preserveAspectRatio' on the 'image' element starts with 'defer',
the 'preserveAspectRatio' attribute on the root element in
the referenced SVG image is also ignored (see 'preserveAspectRatio'
for details).
Instead, the 'preserveAspectRatio' attribute on
the referencing 'image'
element defines how the SVG image content is fitted into the
viewport and the 'clip' and 'overflow' properties on the 'image' element define how the SVG
image content is clipped (or not) relative to the viewport.
The value of the 'viewBox' attribute to use when
evaluating the 'preserveAspectRatio' attribute is
defined by the referenced content. For content that clearly
identifies a viewBox (e.g. an SVG file with the 'viewBox' attribute on the
outermost svg element) that value should be used. For most
raster content (PNG, JPEG) the bounds of the image should be
used (i.e. the 'image'
element has an implicit 'viewBox' of '0 0 raster-image-width
raster-image-height'). Where no value is readily available
(e.g. an SVG file with no 'viewBox' attribute on the
outermost svg element) the 'preserveAspectRatio' attribute is
ignored, and only the translation due to the 'x' & 'y' attributes of the viewport is
used to display the content.
For example, if the image element referenced a PNG or JPEG
and preserveAspectRatio="xMinYMin
meet", then the aspect ratio of the raster would be
preserved (which means that the scale factor from image's
coordinates to current user space coordinates would be the same
for both X and Y), the raster would be sized as large as
possible while ensuring that the entire raster fits within the
viewport, and the top/left of the raster would be aligned with
the top/left of the viewport as defined by the attributes 'x', 'y', 'width' and 'height' on the 'image' element. If the value
of 'preserveAspectRatio' was 'none'
then aspect ratio of the image would not be preserved. The
image would be fitted such that the top/left corner of the
raster exactly aligns with coordinate ('x', 'y') and the bottom/right corner of
the raster exactly aligns with coordinate ('x'+'width', 'y'+'height').
The resource referenced by the 'image' element represents a
separate document which generates its own parse tree and
document object model (if the resource is XML). Thus, there is
no inheritance of properties into the image.
Unlike 'use', the 'image' element cannot reference
elements within an SVG file.
The x-axis coordinate of one corner of the rectangular
region into which the referenced document is placed.
If the attribute is not specified, the effect is as if a
value of '0' were specified. Animatable:
yes.
The y-axis coordinate of one corner of the rectangular
region into which the referenced document is placed.
If the attribute is not specified, the effect is as if a
value of '0' were specified. Animatable:
yes.
The width of the rectangular region into which the
referenced document is placed.
A negative value is an error (see Error processing).
A value of zero disables rendering of the element. Animatable:
yes.
The height of the rectangular region into which the
referenced document is placed.
A negative value is an error (see Error processing).
A value of zero disables rendering of the element. Animatable:
yes.
Attributes 'requiredFeatures', 'requiredExtensions' and 'systemLanguage' act as tests and
return either true or false results. The 'switch' renders the first of
its children for which all of these attributes test true. If
the given attribute is not specified, then a true value is
assumed.
Similar to the 'display' property, conditional processing
attributes only affect the direct rendering of elements and do
not prevent elements from being successfully referenced by
other elements (such as via a 'use').
The 'switch' element evaluates
the 'requiredFeatures', 'requiredExtensions' and
'systemLanguage' attributes on its direct child elements in
order, and then processes and renders the first child for which these
attributes evaluate to true. All others will be bypassed and therefore
not rendered. If the child element is a container element such as a
'g', then the entire subtree is either processed/rendered or
bypassed/not rendered.
Note that the values of properties 'display' and
'visibility' have no effect on 'switch' element
processing. In particular, setting 'display' to
none on a child of a 'switch' element
has no effect on true/false testing associated with 'switch'
element processing.
The value is a list of feature strings, with the
individual values separated by white space. Determines
whether all of the named features are supported by
the user agent. Only feature strings defined in the Feature String appendix are
allowed. If all of the given features are supported, then
the attribute evaluates to true; otherwise, the current
element and its children are skipped and thus will not be
rendered. Animatable:
no.
If the attribute is not present, then its implicit return
value is "true". If a null string or empty string value is
given to attribute 'requiredFeatures', the attribute
returns "false".
'requiredFeatures' is often
used in conjunction with the 'switch' element. If the 'requiredFeatures' is used in other
situations, then it represents a simple switch on the given
element whether to render the element or not.
The 'requiredExtensions'
attribute
The 'requiredExtensions'
attribute defines a list of required language extensions.
Language extensions are capabilities within a user agent that
go beyond the feature set defined in this specification. Each
extension is identified by an IRI reference.
Definition of requiredExtensions:
requiredExtensions =
list-of-extensions
The value is a list of IRI references which
identify the required extensions, with the individual
values separated by white space. Determines whether all of
the named extensions are supported by the user
agent. If all of the given extensions are supported, then
the attribute evaluates to true; otherwise, the current
element and its children are skipped and thus will not be
rendered. Animatable:
no.
If a given IRI
reference contains white space within itself, that white
space must be escaped.
If the attribute is not present, then its implicit return
value is "true". If a null string or empty string value is
given to attribute 'requiredExtensions', the attribute
returns "false".
'requiredExtensions' is often
used in conjunction with the 'switch' element. If the 'requiredExtensions' is used in other
situations, then it represents a simple switch on the given
element whether to render the element or not.
The IRI names for the extension should include versioning
information, such as "http://example.org/SVGExtensionXYZ/1.0",
so that script writers can distinguish between different
versions of a given extension.
The 'systemLanguage' attribute
The attribute value is a comma-separated list of language
names as defined in BCP 47
[BCP47].
Evaluates to "true" if one of the languages indicated by
user preferences exactly equals one of the languages given in
the value of this parameter, or if one of the languages
indicated by user preferences exactly equals a prefix of one of
the languages given in the value of this parameter such that
the first tag character following the prefix is "-".
Evaluates to "false" otherwise.
Note: This use of a prefix matching rule does not imply that
language tags are assigned to languages in such a way that it
is always true that if a user understands a language with a
certain tag, then this user will also understand all languages
with tags for which this tag is a prefix.
The prefix rule simply allows the use of prefix tags if this
is the case.
Implementation note: When making the choice of linguistic
preference available to the user, implementers should take into
account the fact that users are not familiar with the details
of language matching as described above, and should provide
appropriate guidance. As an example, users may assume that on
selecting "en-gb", they will be served any kind of English
document if British English is not available. The user
interface for setting user preferences should guide the user to
add "en" to get the best matching behavior.
Multiple languages MAY be listed for content that is
intended for multiple audiences. For example, content that is
presented simultaneously in the original Maori and English
versions, would call for:
<text systemLanguage="mi, en"><!-- content
goes here --></text>
However, just because multiple languages are present within
the object on which the 'systemLanguage' test
attribute is placed, this does not mean that it is intended for
multiple linguistic audiences. An example would be a beginner's
language primer, such as "A First Lesson in Latin," which is
clearly intended to be used by an English-literate audience. In
this case, the 'systemLanguage' test attribute
should only include "en".
Authoring note: Authors should realize that if several
alternative language objects are enclosed in a 'switch', and none of them
matches, this may lead to situations where no content is
displayed. It is thus recommended to include a "catch-all"
choice at the end of such a 'switch' which is acceptable in
all cases.
If the attribute is not present, then its implicit return
value is "true". If a null string or empty string value is
given to attribute 'systemLanguage', the attribute returns
"false".
'systemLanguage' is often used
in conjunction with the 'switch' element. If the 'systemLanguage' is used in other
situations, then it represents a simple switch on the given
element whether to render the element or not.
Applicability of test attributes
The following list describes the applicability of the test
attributes to the elements that do not directly produce
rendering.
Specifying whether external resources are required for
proper rendering
Documents often reference and use the contents of other
files (and other Web resources) as part of their rendering. In
some cases, authors want to specify that particular resources
are required for a document to be considered correct.
Attribute 'externalResourcesRequired' is available
on all container elements and to all elements which potentially
can reference external resources. It specifies whether
referenced resources that are not part of the current document
are required for proper rendering of the given container
element or graphics element.
Attribute definition:
externalResourcesRequired =
"false | true"
false
(The default value.) Indicates that resources
external to the current document are optional. Document
rendering can proceed even if external resources are
unavailable to the current element and its
descendants.
true
Indicates that resources external to the current
document are required. If an external resource is not
available, progressive rendering is suspended, the
document's SVGLoad event is not
fired and the animation timeline does not begin until
that resource and all other required resources become
available, have been parsed and are ready to be
rendered. If a timeout event occurs on a required
resource, then the document goes into an error state
(see Error
processing). The document remains in an error state
until all required resources become available.
This attribute applies to all types of resource references,
including style sheets, color profiles (see Color profile
descriptions) and fonts specified by an IRI reference using a 'font-face' element or a CSS
@font-face specification. In particular, if an element sets
externalResourcesRequired="true",
then all style sheets must be available since any style sheet
might affect the rendering of that element.
Attribute 'externalResourcesRequired' is not
inheritable (from a sense of attribute value inheritance), but
if set on a container element, its value will apply to all
elements within the container.
Because setting externalResourcesRequired="true" on a
container element will have the effect of disabling progressive
display of the contents of that container, if that container
includes elements that reference external resources, tools that generate
SVG content are cautioned against simply setting externalResourcesRequired="true" on
the outermost svg element on a universal
basis. Instead, it is better to specify externalResourcesRequired="true" on
those particular graphics elements or container elements which
specifically need the availability of external resources in order to
render properly.
Specifies a base IRI other than the base IRI of the
document or external entity. Refer to the XML Base
specification [XML-BASE]. Animatable:
no.
The 'xml:lang' and
'xml:space' attributes
Elements that might contain character data content have
attributes 'xml:lang' and 'xml:space'.
Attribute definitions:
xml:lang = "languageID"
Standard XML attribute to specify the language (e.g.,
English) used in the contents and attribute values of
particular elements. Refer to the Extensible Markup
Language (XML) 1.0 Recommendation [XML10]. Animatable:
no.