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Short URL: http://html5.org/r/1972

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SVNBugCommentTime (UTC)
1972[Authors] [Conformance Checkers] Try a new way of handling images that the author doesn't know much about.2008-08-04 07:52
Index: source
===================================================================
--- source	(revision 1971)
+++ source	(revision 1972)
@@ -13123,13 +13123,13 @@
   that mitigate this attack.</p>
 
   <p>Once the resource has been fetched, if the image is a valid and
-  supported image, the user agent must <span>fire a <code
-  title="event-load">load</code> event</span> on the <code>img</code>
-  element (this happens after <code
-  title="dom-img-complete">complete</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 <span>fire an <code
+  supported image, then the image is said to be <i>available</i>; the
+  user agent must <span>fire a <code title="event-load">load</code>
+  event</span> on the <code>img</code> element (this happens after
+  <code title="dom-img-complete">complete</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 <span>fire an <code
   title="event-error">error</code> event</span> on the
   <code>img</code> element.</p>
 
@@ -13160,40 +13160,165 @@
 
   <hr>
 
-  <p>The element represents the image specified by the <code
-  title="attr-img-src">src</code> attribute.</p>
+  <p>What an <code>img</code> element represents depends on the <code
+  title="attr-img-src">src</code> attribute and the <code
+  title="attr-img-alt">alt</code> attribute.</p>
 
-  <p>When the <code title="attr-img-alt">alt</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>
+  <dl class="switch">
 
-  <p>When the <code title="attr-img-alt">alt</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">alt</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>
+   <dt>If the <code title="attr-img-src">src</code> attribute is set
+   and the <code title="attr-img-alt">alt</code> attribute is set to
+   the empty string</dt>
 
-  <p>When the <code title="attr-img-alt">alt</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>
+   <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">src</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>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is set
+   and the <code title="attr-img-alt">alt</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 (})</dt>
+
+   <dd>
+
+    <p>The image is a key part of the content; the <code
+    title="attr-img-alt">alt</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">src</code>
+    attribute.</p>
+
+    <p>Otherwise, the element represents the text given by the <code
+    title="attr-img-alt">alt</code> attribute. User agents may provide
+    the user with a notification that an image is present but has been
+    omitted from the rendering.</p>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is set
+   and the <code title="attr-img-alt">alt</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 (})</dt>
+
+   <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">alt</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">src</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">alt</code> attribute).</p>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is set
+   and the <code title="attr-img-alt">alt</code> attribute is not</dt>
+
+   <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">src</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 may display
+    some sort of indicator that the image is not being rendered.</p>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is not
+   set and the <code title="attr-img-alt">alt</code> attribute is set
+   to the empty string</dt>
+
+   <dd>
+
+    <p>The element represents nothing.</p>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is not
+   set and the <code title="attr-img-alt">alt</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 (})</dt>
+
+   <dd>
+
+    <p>The element represents the text given by the <code
+    title="attr-img-alt">alt</code> attribute.</p>
+
+   </dd>
+
+   <dt>If the <code title="attr-img-src">src</code> attribute is not
+   set and the <code title="attr-img-alt">alt</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 (})</dt>
+
+   <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">alt</code> attribute).</p>
+
+   </dd>
+
+   <dt>If neither the <code title="attr-img-src">src</code> attribute
+   nor the <code title="attr-img-alt">alt</code> attribute are
+   set</dt>
+
+   <dd>
+
+    <p>The element represents nothing.</p>
+
+   </dd>
+
+  </dl>
+
   <p>The <code title="attr-img-alt">alt</code> attribute does not
   represent advisory information. User agents must not present the
   contents of the <code title="attr-img-alt">alt</code> attribute in
   the same way as content of the <code title="attr-title">title</code>
   attribute.</p>
 
-  <p>If the <code title="attr-img-src">src</code> attribute is
-  omitted, the image represents whatever string is given by the
-  element's <code title="attr-img-alt">alt</code> attribute, if any,
-  or nothing, if that attribute is empty or absent.</p>
+  <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>
 
   <p>The <em>contents</em> of <code>img</code> elements, if any, are
   ignored for the purposes of rendering.</p>
@@ -13309,6 +13434,21 @@
 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">
@@ -13359,6 +13499,7 @@
   </div>
 
 
+
   <h5 id="alt">Requirements for providing text to act as an alternative for images</h5>
 
   <p>The requirements for the <code title="attr-img-alt">alt</code>
@@ -13681,13 +13822,14 @@
     text 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">alt</code> attribute may be omitted, but the
-    <code title="attr-img-alt">alt</code> attribute should be
-    included, with a useful value, if at all possible.</p>
+    title="attr-img-alt">alt</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">alt</code> attribute must not be
-    specified with an empty value.</p>
+    omitted or specified with an empty value.</p>
 
     <div class="example">
 
@@ -13708,11 +13850,15 @@
  &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>
 
@@ -13729,7 +13875,7 @@
      describe a 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>
@@ -13758,8 +13904,9 @@
     are using a text-only 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">alt</code> attribute is only allowed to be
-    omitted when no alternative text is available and none can be made
+    title="attr-img-alt">alt</code> 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>
 
    </dd>
@@ -13785,6 +13932,11 @@
 
   </dl>
 
+  <p>The <code title="attr-img-alt">alt</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.</p>
 
 
 

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