Append comma to markup

[wjm]

Hi Jay,
The following gives what I 'think' you want, but why it does what it 
does I have no idea. I thought that LP would choke on two 'title' 
statements in the header, and why the \title in the markup refers back 
to the first 'title' eludes me, and why it doesn't cause an infinite 
loop... ??
Hope this helps?!?
:)
Cheers
Bill

\header
{
title = "Piece in"
title =
\markup
  {
  \fill-line
    {
    \huge \larger \bold \line
      {
      \concat
        {
        \title ", " %note extra space after the comma
          {
          E \hspace #0.25 \flat
          }

        }
      "Opus"
      }
    }
  }

}