map.extent,layer.extent ,map.fullextent 什么关系？

map.extent,layer.extent ,map.fullextent 什么关系？为什么会出现map.extent> map.fullExtent的情况？

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<P>map.extent> map.fullExtent 怎么还会有这种情况？没有见过</P>
<P>You should bear in mind that you cannot set a Map's Extent to be outside it's FullExtent. </P>
<P>If you are setting the Map.Extent properties (e.g. Set Map.Extent = Rectangle), you should be sure that the Left, Right, Top and Bottom properties of your Rectangle are within the Map's FullExtent. </P>
<P>If at least one of the properties lies outside of the FullExtent, then the Map.Extent change will not be successful, and none of the Map.Extent.Left, Map.Extent.Right, Map.Extent.Top, or Map.Extent.Bottom will change.</P>