Comparison of equivalent content facilities on different embedded content elements

The available equivalent (alternate/fallback) content mechanisms on each of the embedded content elements.
element	short equivalent	long equivalent	note
img	`alt`	`longdesc`
object		contents	*
picture		contents	*
video		contents	*
audio		contents	*
canvas		contents	*
embed			*

an asterisk (*) indicates that the title attribute may be used to provide additional content that may provide some (alternate) information when the embedded content is unavailable or unusable for any reason. In other words, though title is not intended as an equivalent (alternate/fallback) facilitiy, it will function as a short fallback when the embedded content is unavailable or unusable for any reason.