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[css-ui-4] Support cursors using a limited version of image-set()
The more generic <<image>> production continues to be allowed but not required. For clarity, since image-set() is a list of images, and since it would itself be used in a list of cursors, this commit rearranges the text editorially a little, in order to limit the confusion about which list we're talking about.
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‎css-ui-4/Overview.bs‎

Lines changed: 117 additions & 102 deletions
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@@ -601,7 +601,7 @@ user resizing of that element.
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<pre class="propdef">
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Name: cursor
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Value: [ [<<url>> [&lt;x&gt; &lt;y&gt;]?,]* <br>
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Value: [ [ <<url>> | <<url-set>> ] [&lt;x&gt; &lt;y&gt;]? ]#? <br>
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[ auto | default | none |<br>
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context-menu | help | pointer | progress | wait | <br>
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cell | crosshair | text | vertical-text | <br>
@@ -611,7 +611,7 @@ Value: [ [<<url>> [&lt;x&gt; &lt;y&gt;]?,]* <br>
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col-resize | row-resize |
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all-scroll |<br>
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zoom-in | zoom-out <br>
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] ]
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]
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Initial: auto
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Applies to: all elements
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Inherited: yes
@@ -655,106 +655,116 @@ Values have the following meanings:
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<dl dfn-type=value dfn-for=cursor id=cursors>
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<dt>image cursors
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<dd>
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<dl>
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<dt><<url>>
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<dd>
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The user agent retrieves the cursor from the resource designated by the URI.
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If the user agent cannot handle the first cursor of a list of cursors,
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it must attempt to handle the second, etc.
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If the user agent cannot handle any user-defined cursor,
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it must use the cursor keyword at the end of the list.
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Conforming user agents may, instead of <<url>>, support <<image>> which is a superset.
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The UA must support the following image file formats:
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<ul>
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<li>
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PNG, as defined in [[!PNG]]
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<li>
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SVG, as defined in [[!SVG11]],
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in <a href="https://www.w3.org/TR/SVG2/conform.html#secure-static-mode">secure static mode</a> [[!SVG2]],
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if it has a [=natural size=].
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<li>
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any other non-animated image file format that they support
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for <<image>> in other properties,
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such as the 'background-image' property
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</ul>
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In addition, the UA should support the following image file formats:
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<ul>
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<li>
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SVG, as defined in [[!SVG11]],
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in <a href="https://www.w3.org/TR/SVG2/conform.html#secure-animated-mode">secure animated mode</a> [[!SVG2]],
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if it has a [=natural size=].
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<li>
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any other animated image file format that they support
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for <<image>> in other properties,
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such as the 'background-image' property
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</ul>
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The UA may also support additional file formats,
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including SVG, as defined in [[!SVG11]],
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in secure static mode or secure animated mode [[!SVG2]],
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even if it does not have a [=natural size=].
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Note: The CSS Working Group initially intended support for all SVG,
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naturally sized or not.
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Support for non-naturally sized SVG was downgraded from mandatory to optional due
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to lack of implementations.
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Note: At the time of writing this specification (spring 2015),
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the only file formats supported for cursors in common desktop browsers are
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the .ico and .cur file formats, as designed by Microsoft.
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For compatibility with legacy content,
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UAs are encouraged to support these,
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even though the lack of an open specification
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makes it impossible to have a normative requirement
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about these formats.
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Some information on these formats can be found
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<a href="https://en.wikipedia.org/wiki/ICO_%28file_format%29">on Wikipedia</a>.
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The <a>default object size</a> for cursor images is
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a UA-defined size that should be based on
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the size of a typical cursor on the UA's operating system.
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The <a>concrete object size</a> is determined using
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the <a>default sizing algorithm</a>.
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If an operating system is
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<strong>incapable</strong> of rendering a cursor above a given size,
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cursors larger than that size must be shrunk to within
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the OS-supported size bounds,
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while maintaining the cursor image's [=natural aspect ratio=], if any.
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The optional &lt;x&gt; and &lt;y&gt; coordinates
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identify the exact position within the image which is the pointer position (i.e., the hotspot).
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<dt>&lt;x&gt;
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<dt>&lt;y&gt;
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<dd>
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Each is a <<number>>.
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The x-coordinate and y-coordinate of the position
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in the cursor's coordinate system (left/top relative)
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which represents the precise position that is being pointed to.
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Note: This specification does not define
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how the coordinate systems of the various types of <<image>> are established,
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and defers these definitions to [[CSS4-IMAGES]].
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If the values are unspecified,
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then the natural hotspot defined inside the image resource itself is used.
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If both the values are unspecific and the referenced cursor has no defined hotspot,
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the effect is as if a value of "0 0" was specified.
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If the coordinates of the hotspot,
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as specified either inside the image resource or
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by &lt;x&gt; and &lt;y&gt; values,
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fall outside of the cursor image,
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they must be clamped (independently) to fit.
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</dl>
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The first (optional) component of the 'cursor' property
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is a list of image-based cursors.
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If the user agent cannot handle the first cursor of a list of cursors,
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it must attempt to handle the second, etc.
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If the user agent cannot handle any of these author-defined cursors,
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it must use the keyword-based cursor at the end of the list.
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Each author-defined image-based cursor is defined by the following values:
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<dl>
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<dt><<url>> | <<url-set>>
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<dd>
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The user agent retrieves the cursor from the resource designated by the <<url>> or <<url-set>>.
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Conforming user agents may, instead of <<url>> and <<url-set>>,
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support <<image>> which is a superset.
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<dfn type>&lt;url-set></dfn> is a limited version of ''image-set()'',
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where only <<url>> and <<url-set>> can be used
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in the part of the <<image-set-option>> sub-production which would normally allow <<image>>.
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The UA must support the following image file formats:
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<ul>
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<li>
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PNG, as defined in [[!PNG]]
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<li>
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SVG, as defined in [[!SVG11]],
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in <a href="https://www.w3.org/TR/SVG2/conform.html#secure-static-mode">secure static mode</a> [[!SVG2]],
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if it has a [=natural size=].
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<li>
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any other non-animated image file format that they support
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for <<image>> in other properties,
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such as the 'background-image' property
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</ul>
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In addition, the UA should support the following image file formats:
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<ul>
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<li>
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SVG, as defined in [[!SVG11]],
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in <a href="https://www.w3.org/TR/SVG2/conform.html#secure-animated-mode">secure animated mode</a> [[!SVG2]],
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if it has a [=natural size=].
702+
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<li>
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any other animated image file format that they support
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for <<image>> in other properties,
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such as the 'background-image' property
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</ul>
708+
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The UA may also support additional file formats,
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including SVG, as defined in [[!SVG11]],
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in secure static mode or secure animated mode [[!SVG2]],
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even if it does not have a [=natural size=].
713+
714+
Note: The CSS Working Group initially intended support for all SVG,
715+
naturally sized or not.
716+
Support for non-naturally sized SVG was downgraded from mandatory to optional due
717+
to lack of implementations.
718+
719+
Note: At the time of writing this specification (spring 2015),
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the only file formats supported for cursors in common desktop browsers are
721+
the .ico and .cur file formats, as designed by Microsoft.
722+
For compatibility with legacy content,
723+
UAs are encouraged to support these,
724+
even though the lack of an open specification
725+
makes it impossible to have a normative requirement
726+
about these formats.
727+
Some information on these formats can be found
728+
<a href="https://en.wikipedia.org/wiki/ICO_%28file_format%29">on Wikipedia</a>.
729+
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The <a>default object size</a> for cursor images is
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a UA-defined size that should be based on
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the size of a typical cursor on the UA's operating system.
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The <a>concrete object size</a> is determined using
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the <a>default sizing algorithm</a>.
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If an operating system is
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<strong>incapable</strong> of rendering a cursor above a given size,
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cursors larger than that size must be shrunk to within
739+
the OS-supported size bounds,
740+
while maintaining the cursor image's [=natural aspect ratio=], if any.
741+
742+
The optional &lt;x&gt; and &lt;y&gt; coordinates
743+
identify the exact position within the image which is the pointer position (i.e., the hotspot).
744+
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<dt>&lt;x&gt;
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<dt>&lt;y&gt;
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<dd>
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Each is a <<number>>.
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The x-coordinate and y-coordinate of the position
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in the cursor's coordinate system (left/top relative)
751+
which represents the precise position that is being pointed to.
752+
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Note: This specification does not define
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how the coordinate systems of the various types of <<image>> are established,
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and defers these definitions to [[CSS4-IMAGES]].
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If the values are unspecified,
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then the natural hotspot defined inside the image resource itself is used.
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If both the values are unspecific and the referenced cursor has no defined hotspot,
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the effect is as if a value of "0 0" was specified.
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If the coordinates of the hotspot,
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as specified either inside the image resource or
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by &lt;x&gt; and &lt;y&gt; values,
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fall outside of the cursor image,
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they must be clamped (independently) to fit.
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</dl>
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<dt>general purpose cursors
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<dd>
@@ -2452,6 +2462,11 @@ the following normative changes have been made:
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<ul>
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<li>
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Introduce a definition for the 'pointer-events' property.
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<li>
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Extend the image types required to be supported for the 'cursor' property
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from just <<url>> to <<url>> and <<url-set>>.
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(Support for the broader <<image>> type remains allowed but optional.)
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</ul>
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<h3 id=changes-24-1-2020 class=no-num>Changes from the

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