message: docs: Fix concrete syntax dangling reference.
diff: @@ -69,7 +69,7 @@ Modules are lists of zero-or-more definitions. Definitions within a module must
  > <sub>Grammar:</sub>
  >
  > _item_ ::=\
  -> &emsp;|&ensp;_constant-type-definition_\
  +> &emsp;|&ensp;_constant-definition_\
  > &emsp;|&ensp;_struct-type-definition_
  >
  > _module_ ::=\
  