each dimension can only have one default axis

base_classes/NXdata.nxdl.xml

@@ -383,7 +383,7 @@
 			The ``axes`` attribute is a list of strings which are the names of the :ref:`AXISNAME </NXdata/AXISNAME-field>` fields
 			to be used as the default axis along all :ref:`DATA </NXdata/DATA-field>` dimensions. As a result the length must
 			be equal to the rank of the :ref:`DATA </NXdata/DATA-field>` fields. The string "." can be used for
-			dimensions without default axes.
+			dimensions without a default axis.
 
 			.. note::  When ``axes`` contains multiple strings, it must be saved as an actual array
 				of strings and not a single comma separated string.