SVG 2 – 09 July 2015 TopContentsPreviousNextElementsAttributesProperties

Chapter 11: Embedded Content

Contents

SVG 2 Requirement: - Have a video element in SVG namespace with the same characteristics as the HTML 5 video element.
- Support 'canvas' element in SVG 2
- the 'video' element
- the 'audio' element
Resolution: - Keep the "Allow video elements to have captions, tracks, etc" SVG 2 requirement.
- The "Provide a way to control audio level and playback" SVG 2 requirement does not need any action, as we will get this functionality from HTMLAudioElement.
- We will keep the "Allow video elements to have captions, tracks, etc" SVG 2 requirement.
- Add an iframe-like element to SVG that includes declarative support for dynamic loading
Purpose: To allow various HTML embedded content elements to be used directly in SVG and support dynamic loading of content.
Owner: stakagi (ACTION-3432)

11.1. Overview

SVG supports embedded content similar to the HTML5's embedded content. Embedded content is content that imports another resource into the document, or content from another vocabulary that is inserted into the document.

The embedded content elements which SVG supports are image, video, audio, iframe, canvas and foreignObject.

Except canvas and foreignObject, embedded content supports Resource Priorities for hinting of downloading external resources. The normative reference is Resource Priorities.

Stakagi: The current Resource Priorities draft does not support embedded content elements which is going to be added by SVG2.0, such as video. Besides, the consideration for mapping and its tiling use cases may be insufficient. It may be better to describe detailed behavior of Resource Priorities in SVG at SVG specifications.

11.2. Placement and scaling of the referenced resource

Some embedding elements which refer to an external resource establish a new viewport for the referenced content as described in Establishing a new SVG viewport. The bounds for the new viewport are defined by attributes x, y, width and height. The placement and scaling of the referenced resource are controlled by the preserveAspectRatio attribute on the corresponding element.

Brian: I think it's not obvious that we want to add preserveAspectRatio to these elements since CSS3 Images is trying to define similar functionality. Maybe make this an issue?

Attribute definitions:

Name Value Initial value Animatable
x, y <length> 0 yes
width, height <length> | auto 0 yes

The x, y, width and height attributes specify the rectangular region into which the referenced resource is placed.

A negative value for width and height is invalid (see Error processing). A value of zero for either attribute disables rendering of the element.

The 'auto' value for width and height is used to size the corresponding element automatically based on the intrinsic size or aspect ratio of the referenced resource. If the intrinsic aspect ratio of the referenced resource is unknown, it is assumed to be 2:1. If the intrinsic size of the referenced resource is unknown, it is assumed to be 300x150, just as is required for CSS replaced elements. If 'auto' is specified for just one of width or height, then the other is determined based on the intrinsic aspect ratio. The automatically determined width and height values are interpreted as user units, and are reflected in the x and y IDL attributes as SVG_LENGTHTYPE_NUMBER values.

Since the pixel coordinate system which some embedded contents has is not always equivalent SVG coordinate system to embed, canvas and iframe have intrinsic width and height as canvasWidth and canvasHeight for canvas, frameWidth and frameHeight for iframe to assign its intrinsic content size.

11.3. The ‘image’ element

image
Categories:
Graphics element, graphics referencing element, structurally external element
Content model:
Any number of the following elements, in any order:clipPath, marker, mask, script
Attributes:
DOM Interfaces:

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.

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.

Why does it make sense to override ‘clip’ but not ‘clip-path’?

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.

We should say how the use of an #xywh media fragment interacts with the the above.

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.

SVG 2 Requirement: Support auto-sized images.
Resolution: We will allow auto-sized images in SVG 2.
Purpose: To allow raster images to use their own size without the need to set width and height.
Owner: Cameron (ACTION-3340)
SVG 2 Requirement: Support selecting part of an image for display.
Resolution: We will have a method for ‘image’ to select a part of an image to display, maybe by allowing ‘viewBox’ on it.
Purpose: To allow selection of part of an image without requiring the author to manually slice the image.
Owner: Nobody
SVG 2 Requirement: Support the ‘object-fit’ and ‘object-position’ properties from css3-images.
Resolution: SVG 2 will depend on CSS3 Image Values and CSS4 Image Values.
Purpose: To align with the CSS way of specifying image fitting that preserveAspectRatio provides.
Owner: Cameron or Erik (no action)

Attribute definitions:

Name Value Initial value Animatable
crossorigin [ anonymous | use-credentials ] anonymous yes

The crossorigin attribute is a CORS settings attribute, and unless otherwise specified follows the same processing rules as in html [HTML].

Name Value Initial value Animatable
href URL [URL] (none) yes

An URL reference identifying the image to render. Refer to the common handling defined for URL reference attributes and deprecated XLink attributes.

To get the referenced resource, do a potentially CORS-enabled fetch of the absolute URL that resulted from the earlier step, with the mode being the current state of the element's crossorigin attribute, the origin being the origin of the image element's Document, and the default origin behaviour set to taint. For origin, the rules defined for the html 'img' element apply the same way to the svg image element.

Name Value Initial value Animatable
preserveAspectRatio defer? <align> [ meet | slice ]? xMidYMid meet yes

Specifies the fitting behavior when the aspect ratio of the referenced image does not match the aspect ratio of the rectangle it is placed in. See the definition of preserveAspectRatio for details.

An example:

<?xml version="1.0" standalone="no"?>
<svg width="4in" height="3in"
     xmlns="http://www.w3.org/2000/svg">
  <desc>This graphic links to an external image
  </desc>
  <image x="200" y="200" width="100px" height="100px"
         href="myimage.png">
    <title>My image</title>
  </image>
</svg>

11.4. The ‘video’ element

video
Categories:
Graphics element, graphics referencing element, structurally external element
Content model:
Any number of the following elements, in any order:clipPath, marker, mask, script, source, track
Attributes:
DOM Interfaces:

The video element introduces the function that is almost equivalent to 'video' element of html5.0 into svg. But, from the difference of the model of svg and html, it has some differences. This chapter describe them mainly. Therefore, except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'video' element of html5.0.

To refer a video resource, 'video' element uses src attribute insted of 'href'.

Placement of video resources is established in accordance with Placement and scaling of the referenced resource using ‘x’, ‘y’, ‘width’, ‘height’ and ‘preserveAspectRatio’ attributes.

11.5. The ‘audio’ element

audio
Categories:
Graphics element, graphics referencing element, structurally external element
Content model:
Any number of the following elements, in any order:clipPath, marker, mask, script, source, track
Attributes:
DOM Interfaces:

The audio element introduces the function that is almost equivalent to 'audio' element of html5.0 into svg. Except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'audio' element of html5.0. The 'audio' element is not rendered on screen unless it has 'controls' boolean attribute of true.

If controls boolean attribute is present, the x, y attributes specify the upper left corner of built-in controller. Otherwise those attributes has no effects.

11.6. The ‘iframe’ element

iframe
Categories:
Graphics element, graphics referencing element, structurally external element
Content model:
Any number of the following elements, in any order:clipPath, marker, mask, script
Attributes:
DOM Interfaces:

The iframe element introduces the function that is almost equivalent to 'iframe' element of html5.0 into svg. Except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'iframe' element of html5.0.

The iframe element introduces a new nested browsing context. Placement of browsing context is established in accordance with placement and scaling of the referenced resource using x, y, width, height, frameWidth, frameHeight and preserveAspectRatio attributes.

The frameWidth and frameHeight specifies the natural (intrinsic) size (dimension) of browsing context(in CSS pixel) in non negative value. Unlike from canvas, floating point values are acceptable as intrinsic width and height. (See also CSS Image Values and Replaced Content Module Level 4 #sizing)

If frameWidth or frameHeight attributes are not specified, values of width or height are assigned to corresponding DOM attributes.

Are 'frameWidth' and 'frameHeight' really required? They may only be the same as 'width' and 'height'.

Differ from image element, even if iframe element references an SVG document, placement and scaling is achieved toward browsing context based on its intrinsic size. After that, referred SVG document will be arranged based on initial viewport establishment process for browsing context.

Attribute definitions:

Name Value Initial value Animatable
frameWidth <length> 0 yes
frameHeight <length> 0 yes

11.7. The ‘canvas’ element

canvas
Categories:
Graphics element
Content model:
Any number of the following elements, in any order:clipPath, marker, mask, script
Attributes:
DOM Interfaces:

The canvas element introduces the function that is almost equivalent to 'canvas' element of html5.0 into svg. Except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'canvas' element of html5.0.

The canvasWidth and canvasHeight specifies the natural size(dimension) of canvas object in non negative integer. Therefore it corresponds to html:canvas's 'width' and 'height'. (See also CSS Image Values and Replaced Content Module Level 4 #sizing)

On the other hand, x, y, width and height attributes specify the rectangular region into which the canvas object is placed considering preserveAspectRatio attribute in accordance with Placement and scaling of the referenced resource.

If canvasWidth or canvasHeight are not specified, INT(width) or INT(height) are assigned to corresponding DOM attributes. In this case, if width or height is less than 1 , then the canvas object is not generated.

Attribute definitions:

Name Value Initial value Animatable
canvasWidth <length> 0 yes
canvasHeight <length> 0 yes

11.8. Foreign namespaces and private data

SVG allows inclusion of elements from foreign namespaces anywhere with the SVG content. In general, the SVG user agent will include the unknown elements in the DOM but will otherwise ignore unknown elements. (The notable exception is described under Embedding Foreign Object Types.)

Additionally, SVG allows inclusion of attributes from foreign namespaces on any SVG element. The SVG user agent will include unknown attributes in the DOM but with otherwise ignore unknown attributes.

SVG's ability to include foreign namespaces can be used for the following purposes:

To illustrate, a business graphics authoring application might want to include some private data within an SVG document so that it could properly reassemble the chart (a pie chart in this case) upon reading it back in:

<?xml version="1.0" standalone="yes"?>
<svg width="4in" height="3in"
     xmlns = 'http://www.w3.org/2000/svg'>
  <defs>
    <myapp:piechart xmlns:myapp="http://example.org/myapp"
                    title="Sales by Region">
      <myapp:pieslice label="Northern Region" value="1.23"/>
      <myapp:pieslice label="Eastern Region" value="2.53"/>
      <myapp:pieslice label="Southern Region" value="3.89"/>
      <myapp:pieslice label="Western Region" value="2.04"/>
      <!-- Other private data goes here -->
    </myapp:piechart>
  </defs>
  <desc>This chart includes private data in another namespace
  </desc>
  <!-- In here would be the actual SVG graphics elements which
       draw the pie chart -->
</svg>

11.9. Embedding foreign object types

One goal for SVG is to provide a mechanism by which other XML language processors can render into an area within an SVG drawing, with those renderings subject to the various transformations and compositing parameters that are currently active at a given point within the SVG content tree. One particular example of this is to provide a frame for XML content styled with CSS or XSL so that dynamically reflowing text (subject to SVG transformations and compositing) could be inserted into the middle of some SVG content. Another example is inserting a MathML expression into an SVG drawing [MATHML].

The foreignObject element allows for inclusion of a foreign namespace which has its graphical content drawn by a different user agent. The included foreign graphical content is subject to SVG transformations, filters, clipping, masking and compositing.

The contents of foreignObject are assumed to be from a different namespace. Any SVG elements within a foreignObject will not be drawn, except in the situation where a properly defined SVG subdocument with a proper ‘xmlns’ (see Namespaces in XML [XML-NS]) attribute specification is embedded recursively. One situation where this can occur is when an SVG document fragment is embedded within another non-SVG document fragment, which in turn is embedded within an SVG document fragment (e.g., an SVG document fragment contains an XHTML document fragment which in turn contains yet another SVG document fragment).

Usually, a foreignObject will be used in conjunction with the switch element and the requiredExtensions attribute to provide proper checking for user agent support and provide an alternate rendering in case user agent support is not available.

11.10. The ‘foreignObject’ element

foreignObject
Categories:
Graphics element, structurally external element
Content model:
Any elements or character data.
Attributes:
Geometry properties:
DOM Interfaces:

The ‘x’ and ‘y’ attributes define the coordinates of the left and top edges of the 'foreignObject', in the current user coordinate system.

The ‘width’ and ‘height’ attributes define width and height of the 'foreignObject' respectively. A negative value for either attribute is an error (see Error processing). A value of zero for either attribute disables rendering of the element.

An example:

<?xml version="1.0" standalone="yes"?>
<svg width="4in" height="3in"
 xmlns = 'http://www.w3.org/2000/svg'>
  <desc>This example uses the 'switch' element to provide a
        fallback graphical representation of an paragraph, if
        XMHTML is not supported.</desc>
  <!-- The 'switch' element will process the first child element
       whose testing attributes evaluate to true.-->
  <switch>
    <!-- Process the embedded XHTML if the requiredExtensions attribute
         evaluates to true (i.e., the user agent supports XHTML
         embedded within SVG). -->
    <foreignObject width="100" height="50"
                   requiredExtensions="http://example.com/SVGExtensions/EmbeddedXHTML">
      <!-- XHTML content goes here -->
      <body xmlns="http://www.w3.org/1999/xhtml">
        <p>Here is a paragraph that requires word wrap</p>
      </body>
    </foreignObject>
    <!-- Else, process the following alternate SVG.
         Note that there are no testing attributes on the 'text' element.
         If no testing attributes are provided, it is as if there
         were testing attributes and they evaluated to true.-->
    <text font-size="10" font-family="Verdana">
      <tspan x="10" y="10">Here is a paragraph that</tspan>
      <tspan x="10" y="20">requires word wrap.</tspan>
    </text>
  </switch>
</svg>

It is not required that SVG user agent support the ability to invoke other arbitrary user agents to handle embedded foreign object types; however, all conforming SVG user agents would need to support the switch element and must be able to render valid SVG elements when they appear as one of the alternatives within a switch element.

Ultimately, it is expected that commercial Web browsers will support the ability for SVG to embed content from other XML grammars which use CSS or XSL to format their content, with the resulting CSS- or XSL-formatted content subject to SVG transformations and compositing. At this time, such a capability is not a requirement.

11.11. The ‘source’ element

source
Categories:
None
Content model:
Any number of the following elements, in any order:
    script
    Attributes:
    DOM Interfaces:

    The source element allows authors to specify multiple alternative media resources for media elements. Except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'source' element of html5.0.

    11.12. The ‘track’ element

    track
    Categories:
    None
    Content model:
    Any number of the following elements, in any order:
      script
      Attributes:
      DOM Interfaces:

      The track element allows authors to specify explicit external timed text tracks for media elements. Except for any SVG-specific rules explicitly mentioned in this specification, the normative definition for this element is the 'track' element of html5.0.

      11.13. DOM interfaces

      11.13.1. Interface SVGImageElement

      The SVGImageElement interface corresponds to the image element.

      interface SVGImageElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
        readonly attribute SVGAnimatedLength width;
        readonly attribute SVGAnimatedLength height;
        readonly attribute SVGAnimatedPreserveAspectRatio preserveAspectRatio;
        attribute DOMString crossOrigin;
      };
      
      SVGImageElement implements SVGURIReference;
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute x on the given image element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute y on the given image element.
      width (readonly SVGAnimatedLength)
      Corresponds to attribute width on the given image element.
      height (readonly SVGAnimatedLength)
      Corresponds to attribute height on the given image element.
      preserveAspectRatio (readonly SVGAnimatedPreserveAspectRatio)
      Corresponds to attribute preserveAspectRatio on the given image element.
      crossOrigin (DOMString)
      The crossOrigin IDL attribute must reflect the crossorigin attribute on the given image element, limited to only known values.

      11.13.2. Interface SVGVideoElement

      The SVGVideoElement interface corresponds to the video element. This interface introduces the function that is almost equivalent to 'HTMLVideoElement' interface of html5.0 into svg.

      interface SVGVideoElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
        readonly attribute SVGAnimatedLength width;
        readonly attribute SVGAnimatedLength height;
        readonly attribute SVGAnimatedPreserveAspectRatio preserveAspectRatio;
      };
      SVGVideoElement implements HTMLVideoElement;
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute x on the given video element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute y on the given video element.
      width (readonly SVGAnimatedLength)
      Corresponds to attribute width on the given video element.
      height (readonly SVGAnimatedLength)
      Corresponds to attribute height on the given video element.
      preserveAspectRatio (readonly SVGAnimatedPreserveAspectRatio)
      Corresponds to attribute preserveAspectRatio on the given video element.

      11.13.3. Interface SVGAudioElement

      The SVGAudioElement interface corresponds to the audio element. This interface introduces the function that is almost equivalent to 'HTMLAudioElement' interface of html5.0 into svg.

      interface SVGAudioElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
      };
      SVGAudioElement implements HTMLAudioElement;
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute x on the given audio element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute y on the given audio element.

      11.13.4. Interface SVGIframeElement

      The SVGIframeElement interface corresponds to the iframe element. This interface introduces the function that is almost equivalent to 'HTMLIframeElement' interface of html5.0 into svg.

      interface SVGIframeElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
        readonly attribute SVGAnimatedLength width;
        readonly attribute SVGAnimatedLength height;
        readonly attribute SVGAnimatedPreserveAspectRatio preserveAspectRatio;
        readonly attribute SVGAnimatedLength frameWidth;
        readonly attribute SVGAnimatedLength frameHeight;
      };
      
      SVGIframeElement implements HTMLIframeElement;
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute x on the given iframe element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute y on the given iframe element.
      width (readonly SVGAnimatedLength)
      Corresponds to attribute width on the given iframe element.
      height (readonly SVGAnimatedLength)
      Corresponds to attribute height on the given iframe element.
      preserveAspectRatio (readonly SVGAnimatedPreserveAspectRatio)
      Corresponds to attribute preserveAspectRatio on the given iframe element.
      frameWidth (readonly SVGAnimatedLength)
      Corresponds to attribute frameWidth on the given iframe element.
      frameHeight (readonly SVGAnimatedLength)
      Corresponds to attribute frameHeight on the given iframe element.

      11.13.5. Interface SVGCanvasElement

      The SVGCanvasElement interface corresponds to the canvas element. This interface introduces the function that is almost equivalent to 'HTMLCanvasElement' interface of html5.0 into svg.

      interface SVGCanvasElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
        readonly attribute SVGAnimatedLength width;
        readonly attribute SVGAnimatedLength height;
        readonly attribute SVGAnimatedPreserveAspectRatio preserveAspectRatio;
        readonly attribute SVGAnimatedLength canvasWidth;
        readonly attribute SVGAnimatedLength canvasHeight;
      };
      SVGCanvasElement implements HTMLCanvasElement;
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute x on the given canvas element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute y on the given canvas element.
      width (readonly SVGAnimatedLength)
      Corresponds to attribute width on the given canvas element.
      height (readonly SVGAnimatedLength)
      Corresponds to attribute height on the given canvas element.
      preserveAspectRatio (readonly SVGAnimatedPreserveAspectRatio)
      Corresponds to attribute preserveAspectRatio on the given canvas element.
      canvasWidth (readonly SVGAnimatedLength)
      Corresponds to attribute INT(canvasWidth) on the given canvas element.
      canvasHeight (readonly SVGAnimatedLength)
      Corresponds to attribute INT(canvasHeight) on the given canvas element.

      11.13.6. Interface SVGForeignObjectElement

      The SVGForeignObjectElement interface corresponds to the foreignObject element.
      interface SVGForeignObjectElement : SVGGraphicsElement {
        readonly attribute SVGAnimatedLength x;
        readonly attribute SVGAnimatedLength y;
        readonly attribute SVGAnimatedLength width;
        readonly attribute SVGAnimatedLength height;
      };
      Attributes:
      x (readonly SVGAnimatedLength)
      Corresponds to attribute ‘x’ on the given foreignObject element.
      y (readonly SVGAnimatedLength)
      Corresponds to attribute ‘y’ on the given foreignObject element.
      width (readonly SVGAnimatedLength)
      Corresponds to attribute ‘width’ on the given foreignObject element.
      height (readonly SVGAnimatedLength)
      Corresponds to attribute ‘height’ on the given foreignObject element.

      11.13.7. Interface SVGSourceElement

      The SVGSourceElement interface corresponds to the source element. This interface introduces the function that is almost equivalent to 'HTMLSourceElement' interface of html5.0 into svg.

      interface SVGSourceElement : SVGElement { };
      SVGSourceElement implements HTMLSourceElement;

      11.13.8. Interface SVGTrackElement

      The SVGTrackElement interface corresponds to the track element. This interface introduces the function that is almost equivalent to 'HTMLTrackElement' interface of html5.0 into svg.

      interface SVGTrackElement : SVGElement { };
      SVGTrackElement implements HTMLTrackElement;
      SVG 2 – 09 July 2015 TopContentsPreviousNextElementsAttributesProperties