Added optional floor specifier, and refined the element documentation with clear…

…er and more details information.

@@ -591,13 +591,17 @@
             </elem>
 
             <elem name="source" type="string" multiplicity="1">
-                <comment>Estimate source identifier.  If not defined set to "".</comment>
+                <comment>Estimate calculation source identifier.  In multi-function engines like HPE, calculations can be handled by various calculation functions.   This source identifier
+                provides an analytical characterization that enbles a deeper understanding of how the data is processed.  Identifiers can include terms like 'hybrid', 'agnss', 'celldb', 'ecid', 
+                tdoa, rf-base1, rf-base2, slame, etc. Terms are not constant and may be substantially different across systems using this XID struct. </comment>
             </elem>
             <elem name="obstype" type="ObservationType" multiplicity="1">
-                <comment>The last observation type used to create the estimate.</comment>
+                <comment>The last observation type used to create the estimate. In multi-type observables, multiple estimates will be generated with the last estimate usually indicating the last estimate use.  
+                If estimated simultaneously, then the obstype will be the dominant observations (one with the most obversations and/or least uncertainty).  If there is no dominance, then the observation 
+                type is 'undefined'</comment>
             </elem>
             <elem name="tic" type="uint32">
-                <comment>Tic count of the estimate.  Set to zero if not known.</comment>
+                <comment>Tic count of the estimate.  For single transaction sessions, the tic count is always 0.  For multi-transaction sessions, the tic-count will be monotonic increasing.</comment>
             </elem>
             <elem name="epoch" type="datetime" multiplicity="1">
                 <comment>Epoch defines the point in time for which the estimate applies.</comment>
@@ -610,14 +614,20 @@
                 </comment>
             </elem>
             <elem name="confidence" type="float32" multiplicity="1">
-                <comment>The estimate confidence.  Valid range is 0.0 to 1.0</comment>
+                <comment>The estimate confidence. This is the confidence level associated with the uncertainties specified within the shape (e.g. Spheroid). Valid range is 0.0 to 1.0. 
+                Typical values are 0.5 (50% CEP), 0.6827 (1 Std. Dev.), 0.9545 (2 Std. Dev.), 0.9973 (3 Std. Dev.).  For example,  a confidence of 0.6827 and Spheroid horizontal uncertainty of 10 meters 
+                means the about 68% of the time the estimate will be within 10 meters horizontally to the true position.</comment>
             </elem>
             <elem name="shape" type="Shape" multiplicity="1" polymorphic="true">
                 <comment>
-                    The estimate shape result.  The particular shape is determined by the
-                    preferred shapes specified in the BeginCalculation.
+                    The estimate shape result.  In HPE, the particular shape is determined by the  preferred shapes specified in the BeginCalculation. For other systems, the shape 
+                    provided here is based on an external consideration.   Typically only the common spatial types are used: Circle, Ellipse, Spheroid, and Ellispoid shape types.
                 </comment>
             </elem>
+            <elem name="floor" type="Tensor.int16" multiplicity="0..1">
+                Optional floor specifier if availble.  Floor values are specified by local venue mapping information. As general guideline, 0 denotes the ground-level floor.   
+                Negative values denote floors under ground.
+            </elem>
         </struct>
         
         <!-- eventually may be able to support variable sized elements