<p>In some cases, it's appropriate for <em>Up</em> to perform an action rather than navigating to a parent screen. Take for example, the Gmail application for Android 3.0-based tablets. When viewing a mail conversation while holding the device in landscape, the conversation list, as well as the conversation details are presented side-by-side. This is a form of parent-child screen grouping, as discussed in a <a href="multiple-sizes.html">previous lesson</a>. However, when viewing a mail conversation in the portrait orientation, only the conversation details are shown. The <em>Up</em> button is used to temporarily show the parent pane, which slides in from the left of the screen. Pressing the <em>Up</em> button again while the left pane is visible exits the context of the individual conversation, up to a full-screen list of conversations.</p>
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