%%% Do you need some stretch?

\TeX's \verb|\leaders| primitive can be used to fill arbitrary space with a
stretchable line (cf.\ \verb|\hrulefill|).  It is also possible to have an
expandable triple line:

\def\triplefil{%
  \leaders\hrule height4pt depth-3.2pt\hfil \hskip0pt plus-1fil
  \leaders\vrule height1.6pt depth0pt\hfil \hskip0pt plus-1fil
  \leaders\vrule height-.6pt depth1pt\hfil }
\def\triplefilledline#1{%
  \hbox to\hsize{%
    \vrule height4ptdepth3ptwidth.8pt \triplefil \vrule
    height10ptdepth1ptwidth.4pt \enspace\strut#1\enspace \vrule
    height10ptdepth1ptwidth.4pt \triplefil \vrule
    height4ptdepth3ptwidth.8pt } }

\bigskip
\triplefilledline{The St.\ Anford Orchestra}

\bigskip
\triplefilledline{Variations on a Theme by Tchaikovsky}

\beginverbatim
\def\triplefil{%
  \leaders\hrule height4pt depth-3.2pt \hfil \hskip0pt plus-1fil
  \leaders\vrule height1.6pt depth0pt  \hfil \hskip0pt plus-1fil
  \leaders\vrule height-.6pt depth1pt  \hfil }
\def\triplefilledline#1{%
  \hbox to\hsize{%
    \vrule height4ptdepth3ptwidth.8pt \triplefil \vrule
    height10ptdepth1ptwidth.4pt \enspace\strut#1\enspace \vrule
    height10ptdepth1ptwidth.4pt \triplefil \vrule
    height4ptdepth3ptwidth.8pt } }
\triplefilledline{The St.\ Anford Orchestra}
\triplefilledline{Variations on a Theme by Tchaikovsky}
\endverbatim

To understand what happens here one needs to count stretchability of leaders
and glue in \verb|\triplefil|.  It is: 1fil (from \verb|\hfil|) + $-1$fil
(from \verb|\hskip|) + 1fil + $-1$fil + 1fil, which sums up to 1fil.  So when
\TeX\ needs to set \verb|\triplefil| to, say, 37pt it stretches each fil of
glue to that length.  The first leaders become 37pt wide, then comes
\verb|\hskip| to $-37$pt ($-1$fil), and so \TeX\ overprints the second
\verb|\leaders| on the first, and the same repeats with the next glue and
leaders.

This trick opens space for countless variations:

\def\lquadruple{%
    \leaders\hrule height6.2pt depth-6pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\vrule height4.2pt depth-4pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\vrule height2.2pt depth-2pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\vrule height0.2pt depth0pt\hskip0ptplus3fil
}
\def\rquadruple{%
    \leaders\vrule height0.2pt depth0pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\vrule height2.2pt depth-2pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\vrule height4.2pt depth-4pt\hskip0ptplus3fil \hskip0pt plus-2fil
    \leaders\hrule height6.2pt depth-6pt\hskip0ptplus3fil
}
\def\quadfilledline#1{%
  \hbox to\hsize{%
    \lquadruple
    \enspace\strut#1\enspace
    \rquadruple
  }
}

% commented on user request
% \beginverbatim
% \def\lquadruple{%
%     \leaders\hrule height6.2pt depth-6pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\vrule height4.2pt depth-4pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\vrule height2.2pt depth-2pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\vrule height0.2pt depth0pt\hskip0ptplus3fil
% }
% \def\rquadruple{%
%     \leaders\vrule height0.2pt depth0pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\vrule height2.2pt depth-2pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\vrule height4.2pt depth-4pt\hskip0ptplus3fil \hskip0pt plus-2fil
%     \leaders\hrule height6.2pt depth-6pt\hskip0ptplus3fil
% }
% \def\quadfilledline#1{%
%   \hbox to\hsize{%
%     \lquadruple
%     \enspace\strut#1\enspace
%     \rquadruple
%   }
% }
% \endverbatim

\bigskip
\quadfilledline{The St.\ Anford Orchestra}
\bigskip
\quadfilledline{Variations on a Theme by Tchaikovsky}
\bigskip

\endinput
