clarify what duplicate does and its limitations

(cherry picked from commit a6108f8a3dea4d05a197b5c01b0195ff8f56be35)

doc/classes/Resource.xml

@@ -22,7 +22,8 @@
 			<return type="Resource" />
 			<argument index="0" name="subresources" type="bool" default="false" />
 			<description>
-				Duplicates the resource, returning a new resource. By default, sub-resources are shared between resource copies for efficiency. This can be changed by passing [code]true[/code] to the [code]subresources[/code] argument which will copy the subresources.
+				Duplicates the resource, returning a new resource with the exported members copied. [b]Note:[/b] To duplicate the resource the constructor is called without arguments. This method will error when the constructor doesn't have default values.
+				By default, sub-resources are shared between resource copies for efficiency. This can be changed by passing [code]true[/code] to the [code]subresources[/code] argument which will copy the subresources.
 				[b]Note:[/b] If [code]subresources[/code] is [code]true[/code], this method will only perform a shallow copy. Nested resources within subresources will not be duplicated and will still be shared.
 				[b]Note:[/b] When duplicating a resource, only [code]export[/code]ed properties are copied. Other properties will be set to their default value in the new resource.
 			</description>