@Beta
    public long requiredTimestamp() {
        return requiredTimestamp;
    }
<p>Returns the timestamp that the document stored in the backend must match exactly
for the associated document operation to go through, or 0 if no timestamp requirement
is present (i.e. only the selection condition, if present, is checked).</p>

<p>Note: the timestamp should be compared with Long.compareUnsigned(), as it
reflects an unsigned 64-bit integer in the backend.</p>

<p><strong>Note:</strong> this API is currently in Beta.</p>
document/src/main/java/com/yahoo/document/TestAndSetCondition.java