[dcl.attr.contract] Clarify rules on std::contract_violation

Author: jensmaurer

source/declarations.tex

@@ -4596,7 +4596,10 @@
 setting or modifying the violation handler.
 It is \impldef{argument for violation handler}
 how the violation handler is established for a program and
-how the \tcode{std::contract_violation} argument value is set.
+how
+the \tcode{std::contract_violation}\iref{support.contract.cviol} argument value
+is set,
+except as specified below.
 If a precondition is violated, the source location of the violation is
 \impldef{source location of precondition violation}.
 \begin{note}