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[ac] (0) Try a new way of handling images that the author doesn't kno…

…w much about.

git-svn-id: http://svn.whatwg.org/webapps@1972 340c8d12-0b0e-0410-8428-c7bf67bfef74
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Hixie committed Aug 4, 2008
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<h1 id=html-5>HTML 5</h1>

<h2 class="no-num no-toc" id=draft>Draft Recommendation &mdash; 2 August
<h2 class="no-num no-toc" id=draft>Draft Recommendation &mdash; 4 August
2008</h2>

<p>You can take part in this work. <a
attack.

<p>Once the resource has been fetched, if the image is a valid and
supported image, the user agent must <a href="#firing4">fire a <code
title=event-load>load</code> event</a> on the <code><a
href="#img">img</a></code> element (this happens after <code
title=dom-img-complete><a href="#complete">complete</a></code> starts
returning true). If the fetching process fails without a response from the
remote server, or it completes but the image is not a valid or supported
image, the user agent must <a href="#firing5">fire an <code
supported image, then the image is said to be <i>available</i>; the user
agent must <a href="#firing4">fire a <code title=event-load>load</code>
event</a> on the <code><a href="#img">img</a></code> element (this happens
after <code title=dom-img-complete><a href="#complete">complete</a></code>
starts returning true). If the fetching process fails without a response
from the remote server, or it completes but the image is not a valid or
supported image, the user agent must <a href="#firing5">fire an <code
title=event-error>error</code> event</a> on the <code><a
href="#img">img</a></code> element.


<hr>

<p>The element represents the image specified by the <code
title=attr-img-src><a href="#src">src</a></code> attribute.

<p>When the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute is present and its value is the empty string, the image
supplements the surrounding content. In such cases, the image may be
omitted in the rendering without affecting the meaning of the document. If
the image is not available, then the element represents nothing.

<p>When the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute is present and its value is not the empty string, the image is a
graphical equivalent of the string given in the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute. In such
cases, the image may be replaced in the rendering by the string given in
the attribute without significantly affecting the meaning of the document.
If the image is not available, then the element represents that string
instead.
<p>What an <code><a href="#img">img</a></code> element represents depends
on the <code title=attr-img-src><a href="#src">src</a></code> attribute
and the <code title=attr-img-alt><a href="#alt0">alt</a></code> attribute.

<dl class=switch>
<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to the empty string

<dd>
<p>The image is either decorative or supplemental to the rest of the
content, redundant with some other information in the document.</p>

<p>If the image is available and the user agent is configured to display
that image, then the element represents the image specified by the <code
title=attr-img-src><a href="#src">src</a></code> attribute.</p>

<p>Otherwise, the element represents nothing, and may be omitted
completely from the rendering. User agents may provide the user with a
notification that an image is present but has been omitted from the
rendering.</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to a string with at least
one character whose first character is not a U+007B LEFT CURLY BRACKET
character ({) or whose last character is not a U+007D RIGHT CURLY BRACKET
character (})

<dd>
<p>The image is a key part of the content; the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute gives a
textual equivalent or replacement for the image.</p>

<p>If the image is available and the user agent is configured to display
that image, then the element represents the image specified by the <code
title=attr-img-src><a href="#src">src</a></code> attribute.</p>

<p>Otherwise, the element represents the text given by the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute. User agents
may provide the user with a notification that an image is present but
has been omitted from the rendering.</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to a string whose first
character is a U+007B LEFT CURLY BRACKET character ({) and whose last
character is a U+007D RIGHT CURLY BRACKET character (})

<dd>
<p>The image is a key part of the content, and there is no textual
equivalent of the image available. The string consisting of all the
characters between the first and the last character of the value of the
<code title=attr-img-alt><a href="#alt0">alt</a></code> attribute gives
the kind of image (e.g. photo, diagram, user-uploaded image).</p>

<p>If the image is available, the element represents the image specified
by the <code title=attr-img-src><a href="#src">src</a></code> attribute.</p>

<p>If the image is not available or if the user agent is not configured
to display the image, then the user agent should display some sort of
indicator that the image is not being rendered, providing to the user
the information regarding the kind of image that is (as derived from the
<code title=attr-img-alt><a href="#alt0">alt</a></code> attribute).</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is not

<dd>
<p>The image's role in the document is unknown.</p>

<p>If the image is available, the element represents the image specified
by the <code title=attr-img-src><a href="#src">src</a></code> attribute.</p>

<p>When the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute is missing, the image represents a key part of the content.
Non-visual user agents should apply image analysis heuristics to help the
user make sense of the image. If the image is not available, the element
represents some indication that the image is missing.
<p>If the image is not available or if the user agent is not configured
to display the image, then the user agent may display some sort of
indicator that the image is not being rendered.</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is not set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to the empty string

<dd>
<p>The element represents nothing.</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is not set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to a string with at least
one character whose first character is not a U+007B LEFT CURLY BRACKET
character ({) or whose last character is not a U+007D RIGHT CURLY BRACKET
character (})

<dd>
<p>The element represents the text given by the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute.</p>

<dt>If the <code title=attr-img-src><a href="#src">src</a></code>
attribute is not set and the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute is set to a string whose first
character is a U+007B LEFT CURLY BRACKET character ({) and whose last
character is a U+007D RIGHT CURLY BRACKET character (})

<dd>
<p>The user agent should display some sort of indicator that an image is
missing, providing to the user the information regarding the kind of
image that it would be (as derived from the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute).</p>

<dt>If neither the <code title=attr-img-src><a href="#src">src</a></code>
attribute nor the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute are set

<dd>
<p>The element represents nothing.</p>
</dl>

<p>The <code title=attr-img-alt><a href="#alt0">alt</a></code> attribute
does not represent advisory information. User agents must not present the
contents of the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute in the same way as content of the <code title=attr-title><a
href="#title">title</a></code> attribute.

<p>If the <code title=attr-img-src><a href="#src">src</a></code> attribute
is omitted, the image represents whatever string is given by the element's
<code title=attr-img-alt><a href="#alt0">alt</a></code> attribute, if any,
or nothing, if that attribute is empty or absent.
<p>User agents may always provide the user with the option to display any
image, or to prevent any image from being displayed. User agents may also
apply image analysis heuristics to help the user make sense of the image
when the user is unable to make direct use of the image, e.g. due to a
visual disability or because they are using a text terminal with no
graphics capabilities.

<p>The <em>contents</em> of <code><a href="#img">img</a></code> elements,
if any, are ignored for the purposes of rendering.
this time was simply the letter S! How had he not seen that before? It all
came together now. The phone call where Hector had referred to a lion's tail,
the time Marco had stuck his tongue out...&lt;/p></pre>

<p>Here it is not known at the time of publication what the image will be,
only that it will be a coat of arms of some kind, and thus no replacement
text can be provided, and instead only the kind of image is provided:</p>

<pre>&lt;p>The last user to have uploaded a coat of arms uploaded this one:&lt;/p>
&lt;p>&lt;img src="last-uploaded-coat-of-arms.cgi" alt="{user-uploaded coat of arms}">&lt;/p></pre>

<p>Ideally, the author would find a way to provide real replacement text
even in this case, e.g. by asking the previous user. Not providing
replacement text makes the document more difficult to use for people who
are unable to view images, e.g. blind users, or users or very
low-bandwidth connections or who pay by the byte, or users who are forced
to use a text-only Web browser.</p>
</div>

<div class=example>
available. This could be the case, for instance, on a photo upload site,
if the site has received 8000 photos from a user without the user
annotating any of them. In such cases, the <code title=attr-img-alt><a
href="#alt0">alt</a></code> attribute may be omitted, but the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute should be
included, with a useful value, if at all possible.</p>
href="#alt0">alt</a></code> attribute's value must be a description of
the <em>kind</em> of image, surrounded by braces ("{" and "}"). The kind
of image is something along the lines of "photo", "diagram", "painting",
"user-uploaded image", etc.</p>

<p>In any case, if an image is a key part of the content, the <code
title=attr-img-alt><a href="#alt0">alt</a></code> attribute must not be
specified with an empty value.</p>
omitted or specified with an empty value.</p>

<div class=example>
<p>A screenshot in a gallery of screenshots for a new OS, with some
list of open applications, and a clock."></strong>
&lt;legend>Screenshot of a KDE desktop.&lt;/legend>
&lt;/figure></pre>
</div>

<div class=example>
<p>A photo on a photo-sharing site, if the site received the image with
no metadata other than the caption:</p>

<pre>&lt;figure>
<strong>&lt;img src="1100670787_6a7c664aef.jpg"></strong>
<strong>&lt;img src="1100670787_6a7c664aef.jpg" alt="{photo}"></strong>
&lt;legend>Bubbles traveled everywhere with us.&lt;/legend>
&lt;/figure></pre>

Rorschach inkblot test.</p>

<pre>&lt;figure>
<strong>&lt;img src="/commons/a/a7/Rorschach1.jpg"></strong>
<strong>&lt;img src="/commons/a/a7/Rorschach1.jpg" alt="{inkblot test}"></strong>
&lt;legend>A black outline of the first of the ten cards
in the Rorschach inkblot test.&lt;/legend>
&lt;/figure></pre>
browser, or because they are listening to the page being read out by a
hands-free automobile voice Web browser, or simply because they are
blind), the <code title=attr-img-alt><a href="#alt0">alt</a></code>
attribute is only allowed to be omitted when no alternative text is
available and none can be made available, e.g. on automated image
gallery sites.</p>
attribute is only allowed to contain the <em>kind</em> of image rather
than replacement text when no alternative text is available and none can
be made available, e.g. on automated image gallery sites.</p>

<dt>An image in an e-mail or document intended for a specific person who
is known to be able to view images
abilities might not include easily seeing images.</p>
</dl>

<p>The <code title=attr-img-alt><a href="#alt0">alt</a></code> attribute's
value must not start with a U+007B LEFT CURLY BRACKET character ({) and
end with a U+007D RIGHT CURLY BRACKET character (}), unless the attribute
is giving the <em>kind</em> of image rather than replacement text.

<h4 id=the-iframe><span class=secno>4.7.3 </span>The <dfn
id=iframe><code>iframe</code></dfn> element</h4>

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