code: private void detectAndRejectHybridSyntax(final String optionName) {
          if (optionName.contains(ARGUMENT_KEY_VALUE_SEPARATOR)) {
              throw new CommandLineException(String.format("Can't parse option name containing an embedded '=' (%s)", optionName));
          }
      }
docs: Reject attempts to use hybrid Barclay/legacy syntax that contains embedded "=". Most of the time
  this works because jopt accepts "-O=value". But if "value" contains what appears to be tagging
  syntax (ie., an embedded ":"), the tag parser will fail and give misleading error messages. So instead of
  allowing it some cases and having strange failures in others, require users to always use correct
  (Barclay style) syntax.
  @param optionName name of the option being inspected