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+A discriminant value is present more than once.
+
+Erroneous code example:
+
+```compile_fail,E0081
+enum Enum {
+    P = 3,
+    X = 3, // error!
+    Y = 5,
+}
+```
+
+Enum discriminants are used to differentiate enum variants stored in memory.
+This error indicates that the same value was used for two or more variants,
+making it impossible to distinguish them.
+
+```
+enum Enum {
+    P,
+    X = 3, // ok!
+    Y = 5,
+}
+```
+
+Note that variants without a manually specified discriminant are numbered from
+top to bottom starting from 0, so clashes can occur with seemingly unrelated
+variants.
+
+```compile_fail,E0081
+enum Bad {
+    X,
+    Y = 0, // error!
+}
+```
+
+Here `X` will have already been specified the discriminant 0 by the time `Y` is
+encountered, so a conflict occurs.