DOC #1007 MUST use one of the listed storage modes

contributed_definitions/NXxpcs.nxdl.xml

@@ -132,12 +132,12 @@
 
             In short, :math:`g_2` should be ordered according to the roi_map value.  In principle, any format is acceptable if
             the data and its axes are self-describing as per NeXus recommendations. However, the data is preferred in one
-            of the following two formats:
+            of the following two formats (as noted in ``@storage_mode`` below):
 
             * iterable list of linked files (or keys) for each :math:`g_2` with 1 file (key) per :math:`q`, where `q` is called by the nth roi_map value
             * 2D array [#]_ with shape (:math:`g_2`, :math:`q`), where `q` is represented by the nth roi_map value, not the value `q` value
 
-            Note it is expected that "g2" and all quantities following it will be of the same length.
+            Note it is expected that ``g2`` and all quantities following it will be of the same length.
 
             Other formats are acceptable with sufficient axes description.
 
@@ -150,6 +150,7 @@
           <doc>
             storage_mode describes the format of the data to be loaded
 
+            Data must be stored in one of these formats.
             We encourage the documentation of other formats not represented here.
 
             * one array representing entire data set ("one_array")
@@ -253,6 +254,7 @@
           <doc>
             storage_mode describes the format of the data to be loaded
 
+            Data must be stored in one of these formats.
             We encourage the documention of other formats represented here.
           </doc>
           <enumeration>