Ensuring that symmetry operators are lower case strings.

HISTORY.rst

@@ -1,6 +1,10 @@
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 History
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+2024.3.13 -- Handle uppercase X, Y, Z in strings for symmetry operators
+    * the Crystallographic Open Database CIF files seems to use upper case X, Y, Z in
+      explicit symmetry operators. These need to be lowercased in the code.
+
 2023.12.5 -- Bugfixes for symmetry
     * Fixed issue #72, where symmetry was not correctly handled for trigonal and
       hexagonal cells where atoms had coordinates of 1/3 or 2/3.