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[css-mediaqueries-5] nav-controls: Clarify use in a boolean context (closes #7288) #6795

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24 changes: 5 additions & 19 deletions mediaqueries-5/Overview.bs
Original file line number Diff line number Diff line change
Expand Up @@ -2273,25 +2273,11 @@ Detecting UA-supplied navigation controls: the 'nav-controls' feature</h3>
}
}</code></pre>

As this media feature can be used in a [=boolean context=],
the same example can be written with shorter syntax:

<pre><code class=lang-css>
@media (nav-controls) {
#back-button {
display: none;
}
}</code></pre>

Note: Theoretically, the two are not strictly equivalent,
as there could be new values in a future extension of this media feature
other than ''back''
that could match when ''back'' doesn't.
In that case, using the 'nav-controls' feature in a boolean context could be misleading.
However, given that navigation back is arguably the most fundamental navigation operation,
the CSS Working Group does not anticipate
user interfaces with explicit navigation controls but no back button,
so this problem is not expected to occur in practice.
Note: This media feature can also be used in a [=boolean context=], e.g.,
<code class=lang=css>@media (nav-controls)</code>. However, as there could be new values in a future
extension of this media feature other than ''back'', use of the ''nav-controls'' feature in a boolean
context could cause the page to incorrectly interpret some other control as a "back" button, and its
usage is therefore discouraged.
</div>

Whether [=obviously discoverable=] controls are active does not impact the evaluation of this media feature.
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