code: public Swagger2MarkupConfigBuilder withHeaderRegex(String headerRegex) {
          Validate.notNull(headerRegex, "%s must not be null", headerRegex);
          config.headerPattern = Pattern.compile(headerRegex);
          return this;
      }
docs: Specifies the regex pattern to use for grouping paths.
  
  @param headerRegex regex pattern string containing one capture group
  @return this builder
  @throws PatternSyntaxException when pattern cannot be compiled