at is enabled or disabled.
   </p></div>
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<td class="detailHeaderName">HISTORY_CHANGE</td><td class="detailHeaderType">constant</td><td class="detailHeaderRule">&nbsp;</td>
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<code>public static const HISTORY_CHANGE:String = "historyChange"</code><p>
   Dispatched when the history changes.
   If this is a result of a new message arriving, the message descriptor reside in <code