///   node("target", trg).

   ///   node("target", trg).

   ///   attribute("caption", caption).

   ///   attribute("caption", caption).

   ///   run();

   ///   run();

   ///\endcode

   ///\endcode

   ///

   ///

   /// proper type. If a section has an optional name, then it can be

   /// proper type. If a section has an optional name, then it can be

   /// selected for reading by giving an optional name parameter to the

   /// selected for reading by giving an optional name parameter to the

   /// \c nodes(), \c arcs() or \c attributes() functions.

   /// \c nodes(), \c arcs() or \c attributes() functions.

   ///

   ///

   /// The \c useNodes() and \c useArcs() functions are used to tell the reader

   /// The \c useNodes() and \c useArcs() functions are used to tell the reader

     /// parameter. At the reading process, each line of the section

     /// parameter. At the reading process, each line of the section

     /// will be given to the functor object. However, the empty lines

     /// will be given to the functor object. However, the empty lines

     /// and the comment lines are filtered out, and the leading

     /// and the comment lines are filtered out, and the leading

     /// whitespaces are trimmed from each processed string.

     /// whitespaces are trimmed from each processed string.

     ///

     ///

     /// integers, which should be inserted into a vector.

     /// integers, which should be inserted into a vector.

     ///\code

     ///\code

     ///  @numbers

     ///  @numbers

     ///  12 45 23

     ///  12 45 23

     ///  4

     ///  4