Merge remote-tracking branch 'upstream/develop' into hex_lattice

Conflicts:
	src/relaxng/geometry.rnc

docs/source/usersguide/input.rst

@@ -757,7 +757,10 @@ Each ``<cell>`` element can have the following attributes or sub-elements:
     is on the negative side of surface 3 and the positive side of surface 5, the
     bounding surfaces would be given as "-3 5".
 
-    *Default*: None
+    .. note:: The surface attribute/element can be omitted to make a cell fill
+              its entire universe.
+
+    *Default*: No surfaces
 
   :rotation:
     If the cell is filled with a universe, this element specifies the angles in
@@ -1245,7 +1248,7 @@ implemented in openMC:
 ``<plot>`` Element
 ------------------
 
-Each plot must contain a combination of the following attributes or
+Each plot is specified by a combination of the following attributes or
 sub-elements:
 
   :id:
@@ -1266,6 +1269,18 @@ sub-elements:
 
     *Default*: ``cell``
 
+  :level:
+    Universe depth to plot at (optional).  This parameter controls how many
+    universe levels deep to pull cell and material ids from when setting plot
+    colors.  If a given location does not have as many levels as specified,
+    colors will be taken from the lowest level at that location. For example, if
+    ``level`` is set to zero colors will be taken from top-level (universe zero)
+    cells only.  However, if ``level`` is set to 1 colors will be taken from
+    cells in universes that fill top-level fill-cells, and from top-level cells
+    that contain materials.
+
+    *Default*: Whatever the deepest universe is in the model
+
   :origin:
     Specifies the (x,y,z) coordinate of the center of the plot.  Should be three
     floats separated by spaces.