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[css-values-5] Remove chapter on attr() cycles #12009

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Apr 30, 2025
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[css-values-5] Remove chapter on attr() cycles #12009

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63 changes: 0 additions & 63 deletions css-values-5/Overview.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -1890,69 +1890,6 @@ Security</h4>
''--foo: attr(foo type(&lt;number&gt;)); background-image: src(string(var(--foo)))''
needs to be invalid as well.


<h4 id=attr-cycles>
Cycles</h4>

An attribute value may contain ''attr()'' functions,
or other [=arbitrary substitution functions=],
that are substituted during [=parse with a <syntax>=].
This can cause cyclic dependecies,
either by an attribute referring to itself,
through multiple attributes referring to each other,
or through a combination of other [=arbitrary substitution functions=]
(e.g. ''var()'').

For each element, add a node for every attribute on that element
to the graph described in [[css-variables-1#cycles]].
Then, for each attribute <var>attrib</var>,
add edges as follows:

* From <var>attrib</var> to any attributes referenced by ''attr()''
within <var>attrib</var>'s value.
* From <var>attrib</var> to any [=custom properties=] referenced by ''var()''
within <var>attrib</var>'s value.
* From any [=custom property=] that references <var>attrib</var> using ''attr()''
to <var>attrib</var>.

An ''attr()'' referencing an attribute
which is part of a cycle
makes the containing [=declaration=] [=invalid at computed-value time=].

<div class='example'>
In the following,
<code>width</code> is [=invalid at computed-value time=],
because ''attr()'' tries to substitute a value which refers to itself:

<pre class='lang-css'>
div {
width: attr(data-foo type(*));
}
</pre>
<pre class='lang-html'>
&lt;div data-foo="attr(data-foo type(*))">&lt;/div>
</pre>

Note: Even if one (or both) of the ''attr()'' functions had a fallback,
the result would be the same.
</div>

<div class='example'>
Cycles can occur through [=custom properties=];
in the following,
<code>--x</code> and <code>--y</code> are both [=invalid at computed-value time=]:

<pre class='lang-css'>
div {
--x: var(--y);
--y: attr(data-foo type(*));
}
</pre>
<pre class='lang-html'>
&lt;div data-foo="var(--x)">&lt;/div>
</pre>
</div>

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