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Some Definitions

From: <Ehansen7@aol.com>
Date: Tue, 23 Mar 1999 10:26:41 EST
Message-ID: <83511a9b.36f7b2b1@aol.com>
To: w3c-wai-gl@w3.org
Following are a few revised definitions that might be helpful to Ian. I have
tried to have these reflect the latest phone conversation.

Primary Content {EH: New}

"Primary content" is generally the main content intended for the users of a
Web content. It is complemented by "_alternative content_," which is intended
to allow people with disabilities to obtain the full benefit of the message of
the Web content when some or all of the primary content is inaccessible. 

Alternative Content {EH: New, Revised}

"Alternative content" is Web content that intended to allow people with
disabilities to obtain the full benefit of the message of the Web content when
some or all of the _primary content_ is inaccessible. Alternative content
complements primary Web content by providing portions of it
{EH:23Mar99-1023}in a different manner. A Web site with a full repertoire of
alternative content as defined by the guidelines document {EH: Revised again,
22Mar99-1140. Important issue} can have its message received by many
disability groups, including, among others, individuals who rely on audio-only
(blind but not braille-literate) and braille-only (deaf-blind
{EH:23Mar99-1023. changed}. In HTML, an example of alternative content is the
text placed in the "alt" attribute for an image. That text allows a person
with blindness to know the purpose of the image. (The user agent and assistive
technology present the alternative text content via synthesized speech or
braille.) This document emphasizes the importance of text for alternative
content since it can be readily presented in synthesized speech and braille as
well as displayed visually. However, alternative content can be implemented in
other media, such as prerecorded audio and video. {EH: 22Mar99-1140, Recent
revision: deleted last sentence because it is not correct. My old last
sentence: "Two important classes of alternative content include _"equivalents"
and "descriptions"_."} 

Equivalent {EH:23Mar99-1023}

An "equivalent" is a unit of information that, when presented to a user,
provides essentially the same function (or fulfills the same purpose) as
another unit of information. For example, for an audio clip of a conversation
between two people, a text transcript may constitute an text equivalent of the
audio clip. These guidelines emphasize the importance of providing text
equivalents of non-text media (images, prerecorded audio, video), since text
equivalents can be rendered (presented) in so many ways (e.g., braille,
synthesized speech, visually-displayed text). Reversing, the relationship by
providing non-text equivalents (pictures, videos, audio) for text can also
benefit people, especially nonreaders or people who have difficulty reading.
In the context of this document, equivalents are generally intended to serve
as alternatives for portions of the primary content that are inaccessible to
people with disabilities.

{EH: 22Mar99-1140. Revised 23Mar99-1023} For consistency and quality of
presentation (rendering), equivalents are packaged in consistent ways. For
example, in HTML, text equivalents for images are placed in the alt-attribute
of IMG or INPUT elements{EH: Am I saying this correctly?}. If necessary,
longer text equivalents are placed in "long descriptions" (specifically, in
the files for which the URI [Univeral Resource Identifier] is found in the
"longdesc" attribute of various elements). {EH: One could elaborate on this.} 

{EH: Ian. I think that it is a good idea to drop the distinction between
equivalent/description per yesterday's discussion. If necessary, one could
refer to _conventions for different types of text equivalents_ in the
Techniques document.} 

Text Equivalent

A text equivalent is an _equivalent_ that is encoded in text characters.
Received on Tuesday, 23 March 1999 10:33:32 GMT

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