A rendering engine that enables access to alternate content determines,
based on an accessibility mode, a list of focusable elements associated
with a document to be rendered. If the accessibility mode is inactive,
the list of focusable elements includes elements that are, by default,
focusable. If the accessibility mode is active, the list of focusable
elements also includes elements that have associated alternate content,
but that are not, by default, focusable. When an accessibility mode is
active and an element with associated alternate content is selected, the
alternate content is rendered.
