code: public ConfigParseOptions setIncluder(ConfigIncluder includer) {
          if (this.includer == includer)
              return this;
          else
              return new ConfigParseOptions(this.syntax, this.originDescription, this.allowMissing,
                      includer, this.classLoader);
      }
docs: Set a {@link ConfigIncluder} which customizes how includes are handled.
  null means to use the default includer.
  
  @param includer the includer to use or null for default
  @return new version of the parse options with different includer