Extended Description Analysis

The tables below relate information about requirements and implementations of etended descriptions. This is intended to help the community settle on a path. Known relevant resources from which this draws:

Technological Approaches

The following table outlines proposed approaches to provide extended descriptions. Along with a brief description, the table presents pros, cons, and possible ways of mitigating the cons. Whether an approach meets use cases comprehensively enough is a pro / con but that is addressed in the following table, use cases and technological approaches. Approaches also only work if they are implemented, detailed in the third table.

	Description	Pro	Con	Mitigation
description links	Author provides a link to a desciption near the object. Link text is by convention but not requirement "[D]".	Requires no special implementation Long-established technique Simple for authors	Creates undesired visible links Desciption not programatically associated with object User must follow link and potentially lose place	CSS can hide links from default display, but erases universality benefit Description could be associated via an attribute, though the obvious aria-describedby has been ruled out
longdesc	URI to a description is provided in the "longdesc" attribute of the <img> element.	Long-established technique	Only works for <img> Not liked by implementers Usually (though not inherently) still requires user to follow link Indeterminate processing model for URIs to a description on the same page, yet many advocate this pattern
aria-describedby	Pointer to a description on the same page provided on any object via the "aria-describedby" attribute. This is automatically exposed to the accessibility API.	Description in same page Description available to all users	Description lacks rich exposure to user Description bloats page if it's not considered primary content	Specify that UA can follow arc to rich description (but massively changes how this has been implemented) Allow a URI in the value (but creates big processing confusion potential)
aria-describedat	URI to a description is provided in the "aria-describedat" attribute of any object.	Description not loaded if not needed	Not liked by some implementers
figure with details	<figure> contains a <figcaption> which contains a <details> providing the description.	Leverages existing proposed HTML feature	Feature still in proposal stage Overloads the details element Doesn't support external descriptions Comparatively complex to author May be complex to implement or depend on script support long-term for optimal user experience	Add role attribute to clarify overloading Add src attribute to allow external descriptions
figure with details and embedded iFrame	<figure> contains a <figcaption> which contains a <details> which contains an <iframe> that loads the description.	Leverages existing HTML features Supports external description	External description always loads May require special support to get desired user experience
figure with details with src and role attributes	<figure> contains a <figcaption> which contains a <details> which loads an external description from the "src" attribute and clarifies it's a description with the "role" attribute	Leverages existing HTML features with some modification Supports external description Less overloading of <details>	Requires additional engineering of an already only proposed element (<details>) Comparatively complex to author
accessible SVG	Native SVG features provide description.	Most closely associates description with image	Not all describable objects are in SVG
SVG wrapping bitmap	SVG with description loads a raster image for the presentation.	Keeps description with image	Requires SVG and bitmap processing
link in figure caption	Description link provided in <figcaption>.	Simple for authors Description available to all	Not all describable objects have captions
hidden iframe		Uses existing technology	Kludges the iframe
client-side image map		Uses existing technology
web annotations	Description treated as an annotation, externally stored and related to the object.	Description completely separate from object, yet clearly associated with it Multiple descriptions (languages, level of detail) easily supported	Nascent technology Requires an annotation server?

Use cases and technological approaches

The grid below is intended to map known extended description requirements to technological ways to meet them. Approaches that meet more use cases will generally be preferred, though the other pros and cons also need to be considered.

	description links	longdesc	aria-describedby	aria-describedat	figure with details	figure with details and embedded iFrame	figure with details with src and role attributes	accessible SVG	SVG wrapping bitmap	link in figure caption	hidden iframe	client-side image map	web annotations
Not restricted to images	yes	no	yes	yes	?	?	?	no	no	?	no	no	yes
Can hold rich content	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	yes	?	yes
Same technique for different objects	yes	no	yes	yes	?	?	?	no	no	?	?	?	yes
Reusable in multiple content	yes	yes	no	yes	no	yes	yes	no	no	yes	yes	?	yes?
Description clearly associated with object	no	yes	yes	yes	yes	yes	yes	yes	yes	yes	no	yes	yes?
Clear which associated object is the description	no	yes	yes	yes	no	no	yes	yes	yes	no	no	yes?	yes?
Not bloat primary content page	yes	yes	no	yes	no	yes	yes	no	no	yes	yes	?	yes
Not required to be visible in standard content view	yes	yes	?	yes	?	?	?	?	?	yes	?	?	yes
Discoverable by AT	no	yes	yes	yes	yes	yes	yes	yes	yes	?	?	yes	?
Available on demand to AT users	no	yes	yes	yes	yes	yes	yes	yes	yes	?	?	yes	yes?
Skippable by AT	yes	yes	?	yes	yes	yes	yes	?	?	yes	?	yes	yes
Able to pass structured content to an additional specialized user agent	yes	yes	no	yes	yes	yes	yes	yes	yes	yes	yes	?	?
Easily usable by non-AT users	yes	no	no	no	no	no	no	?	?	yes	?	yes?	yes?

Technological Approaches Implementation

Information about the known implementation of particular approaches is provided here. An approach that has, or is expected soon to have, more implementation will tend to be preferred. Note: implementation information below refers to implementation needed to make the description available to assistive technology, not simply implementation of the base feature in mainstream user agents.

Current: already implemented
Underway: in process of being implemented (may include expected timeline)
Planned: tool has plans to implement (may include expected timeline)
No: tool intends not to implement
N/A: special implementation not required

	Webkit	Blink	Gecko	IE	Edge
description links	N/A	N/A	N/A	N/A	N/A
longdesc	No	?	?	?	?
aria-describedby	?	?	?	?	?
aria-describedat	No	?	?	?	?
figure with details	?	?	?	?	?
figure with details and embedded iFrame	Yes?	Yes?	?	?	?
figure with details with src and role attributes	No	?	?	?	?
accessible SVG	?	?	?	?	?
SVG wrapping bitmap	?	?	?	?	?
link in figure caption	?	?	?	?	?
hidden iframe	?	?	?	?	?
image map	?	?	?	?	?
web annotations	?	?	?	?	?

Extended Description Analysis

Technological Approaches

Use cases and technological approaches

Technological Approaches Implementation

Implementation Complexity

Implementation Approach

	Authors	UA
description links	low	N/A
longdesc	med	low
aria-describedby	med	med
aria-describedat	med	low
figure with details	med	low
figure with details and embedded iFrame	high	med
figure with details with src and role attributes	high	med
accessible SVG	high	high
SVG wrapping bitmap	med	high
link in figure caption	low	low
hidden iframe	med	low
image map	med	low
web annotations	high	high

	Uses AAPI	Requires Script
description links	no	no
longdesc	yes	no
aria-describedby	yes	no
aria-describedat	yes	no
figure with details	no	?
figure with details and embedded iFrame	no	?
figure with details with src and role attributes	no	?
accessible SVG	yes	no
SVG wrapping bitmap	yes	no
link in figure caption	no	no
hidden iframe	no	?
image map	no	no
web annotations	no	yes?