Update index.rst

Author: dave-doty

doc/index.rst

@@ -31,14 +31,19 @@ Scadnano provides function to convert design to and from cadnano v2:
 **Important**
 
 All ``cadnanov2`` designs can be imported to scadnano. However **not all scadnano designs can be imported 
-to cadnanov2**, to be exportable to ``cadnanov2`` a scadnano design need to comply with the following points:
-
-* The design cannot feature any :class:`Loopout` or :class:`Extension`, since these are not concepts that exist in ``cadnanov2``.
-* Following ``cadnanov2`` conventions, helices with **even** number must have their scaffold going **forward** and helices with **odd** number **backward**.
-* If you use paranemic crossovers (i.e. crossovers where the domains before and after the crossover are in the same direction), the helices' row number (i.e. not the helices' indexes but their y coordinate) of the domains must have the same parity e.g. rows 0 and 2, or 1 and 3, but not 0 and 1.
-
-Also note that maximum helices offsets can be altered in a ``scadnano`` to ``cadnanov2`` conversion as ``cadnanov2`` needs max offsets to be a multiple of 21 in the hex grid and 32 in the rectangular grid.
-The conversion algorithm will choose the lowest multiple of 21 or 32 which fits the entire design.
+to cadnanov2**; to be exportable to ``cadnanov2`` a scadnano design need to comply with the following constraints:
+
+* The design cannot feature any :class:`Loopout` or :class:`Extension`, since these are not concepts that exist in
+  ``cadnanov2``.
+* Following ``cadnanov2`` conventions, helices with **even** number must have their scaffold going **forward** and
+  helices with **odd** number **backward**.
+* If you use paranemic crossovers (i.e. crossovers where the domains before and after the crossover are in the same
+  direction), the helices' row number (i.e. not the helices' indexes but their y coordinate) of the domains must have
+  the same parity, meaning both even or both odd, for example rows 0 and 2, or 1 and 3, but not 0 and 1.
+
+Also note that maximum helices offsets can be altered in a ``scadnano`` to ``cadnanov2`` conversion as ``cadnanov2``
+needs max offsets to be a multiple of 21 in the hex grid and 32 in the rectangular grid. The conversion algorithm will
+choose the lowest multiple of 21 or 32 which fits the entire design.
 
 The ``cadnanov2`` json format does not embed sequences hence they will be lost after conversion.