The switch element specifies a set of alternative elements from which only one should be chosen. The player evaluates the elements in the order that they occur in the switch. The first element for which the media-type can be decoded and all of the test-attributes evaluate to true is selected, and all other elements in the switch element are excluded.
The switch element has two attributes: "id" and "title." The id attribute simply gives a unique identifier to the element. The title attribute gives advisory information about the element.
The following are examples of test attributes that can be associated with any synchronization
element. These attributes represent Boolean tests. When at least one of the test attributes
evaluates to "false," the element is not chosen in the switch.
"system-birate," which measures the bandwidth available, in bits per second, to the
system. This attribute evaluates to "true" if the bandwidth is equal to or greater than the given
value, and it evaluates to "false" otherwise.
"system-language," which specifies a list of languages. The attribute evaluates to "true" if the
language indicated by the user preferences is equal to one of those in the list, and it
evaluates to "false" otherwise.
"system-screen-size," which gives a screen height and width. The attribute evaluates to "true"
if the SMIL playback engine is capable of displaying a presentation of the given size and "false"
otherwise.
If the "switch" element is a direct or indirect child of the "body" element, it can contain the
following children: animation, audio, img, ref, text, textstream, video, a, par, seq.
