clarify documentation

base_classes/NXtransformations.nxdl.xml

@@ -96,11 +96,6 @@
 		attribute multiplied by the field value, and :math:`R` is defined as a rotation
 		about an axis in the direction of ``vector``, of angle of the field value.
 	</doc>
-	<!-- see: http://wiki.nexusformat.org/Main_Page/NXdetector_2012_10
-		
-		This entire explanation is not clear.
-		-->
-
 	<field name="AXISNAME" nameType="any" units="AXISUNITS" type="NX_NUMBER" maxOccurs="unbounded">
 		<doc>
 			Units need to be appropriate for translation or rotation
@@ -119,15 +114,14 @@
 				values are linear displacements along the axis, ``rotation``,
 				in which case the values are angular rotations around the axis.
 
-				If this attribute is omitted, this is an axis for which there
-				is no motion to be specifies, such as the direction of gravity,
-				or the direction to the source, or a basis vector of a
-				coordinate frame.
+				If this attribute is omitted, this field does not specify a transformation
+				of an object, but is used to document a general axis or direction, 
+				such as the direction of gravity, or of the source. 
+				As such it cannot be used in a depends_on transformation chain.
 			</doc>
 			<enumeration>
 				<item value="translation" />
 				<item value="rotation" />
-				<!-- <item value="general" /> -->
 			</enumeration>
 		</attribute>
 		<attribute name="vector" units="NX_DIMENSIONLESS" type="NX_NUMBER">
@@ -168,17 +162,6 @@
 			at the corresponding positions given in the ``AXISNAME`` field.
 		</doc>
 	</field>
-	<!-- as per NIAC discussion, 13 Oct 2016, we have removed AXISNAME_range as duplicative.	
-	<field name="AXISNAME_range" units="AXISUNITS"  nameType="any" type="NX_NUMBER" minOccurs="0">
-		<doc>
-			AXISNAME_range is a placeholder for a name constructed from the actual
-			name of an axis to which ``_range`` has been appended.
-
-			The values in this optional field are differences between the values
-			in the field AXISNAME_end and the field AXISNAME.
-		</doc>
-	</field>
-	-->
 	<field name="AXISNAME_increment_set" units="AXISUNITS"  nameType="any" type="NX_NUMBER" minOccurs="0">
 		<doc>
 			``AXISNAME_increment_set`` is a placeholder for a name constructed from the actual
@@ -192,4 +175,3 @@
 		</doc>
 	</field>
 </definition>
-