DOC: add additional sorting details to the parrec API docs

Author: grlee77

nibabel/parrec.py

@@ -96,18 +96,28 @@
 ``nibabel.load`` (or ``parrec.load``) should be set to ``True``.  The fields
 that are taken into account during sorting are:
 
-    - image_type_mr  (Re, Im, Mag, Phase)
-    - dynamic scan number
-    - label type  (ASL tag vs. control)
-    - diffusion b value number
-    - gradient orientation number
-    - cardiac phase number
-    - echo number
     - slice number
+    - echo number
+    - cardiac phase number
+    - gradient orientation number
+    - diffusion b value number
+    - label type  (ASL tag vs. control)
+    - dynamic scan number
+    - image_type_mr  (Re, Im, Mag, Phase)
+
+Slices are sorted into the third dimension and the
+order of preference for sorting along the 4th dimension corresponds to the
+order in the list above.  If the image data has more than 4 dimensions these
+will all be concatenated along the 4th dimension.  For example, for a scan with
+two echos and two dynamics, the 4th dimension will have both echos of dynamic 1
+prior to the two echos for dynamic 2.
+
+The``get_volume_labels`` method of the header returns a dictionary containing
+the PAR field labels for this 4th dimension.
 
-If the image data has more than 4 dimensions these will all be concatenated
-along the 4th dimension.  The``get_volume_labels`` method of the header returns
-a dictionary containing the PAR field labels for this 4th dimension.
+The volume sorting described above can be enabled in the parrec2nii command
+utility via the option "--strict-sort".  The dimension info can be exported
+to a CSV file by adding the option "--volume-info".
 """
 from __future__ import print_function, division