docs: public boolean knowsValidationMatcher(String validationMatcherName) {
          // custom libraries:
          if (validationMatcherName.contains(":")) {
              String validationMatcherPrefix = validationMatcherName.substring(0, validationMatcherName.indexOf(':') + 1);
              
              if (!validationMatcherPrefix.equals(prefix)) {
                  return false;
              }
              return members.containsKey(validationMatcherName.substring(validationMatcherName.indexOf(':') + 1, validationMatcherName.indexOf('(')));
          } else {
              // standard citrus-library without prefix:
              return members.containsKey(validationMatcherName.substring(0, validationMatcherName.indexOf('(')));
          }
      }