+/** A legacy exception
+ *
+ * It is defined by a category and a value within that category (as well as
+ * an optional error message).
+ *
+ * This used to be a structure for C exceptions but it has been retrofitted
+ * as a C++ exception and some of its data has been moved in the
+ * @ref WithContextException base class. We should deprecate it and replace it
+ * with either C++ different exceptions or `std::system_error` which already
+ * provides this (category + error code) logic.
+ *
+ * @ingroup XBT_ex_c
+ */