`\thesis@def@extra` now accepts a default definition.

  \fi}

%    \end{macrocode}

% \begin{macro}{\thesis@def@extra}

% The |\thesis@def@extra|\oarg{key}\marg{name} macro defines

% The |\thesis@def@extra|\oarg{definition}\marg{name} macro defines

% the |\thesis@extra@|\textit{name} macro to expand

% to either <<\textit{key}>>, if specified, or to

% <<extra@\textit{name}>>. The macro serves to provide placeholder

% strings for extra data macros. If |\thesis@extra@|\textit{name}

% has already been defined by the user, |\thesis@def@extra| has no

% to either \textit{definition}, if specified, or to

% |\thesis@placeholder@extra@|\textit{name}, where

% |\thesis@placeholder@extra@|\textit{name} is defined to expand to

% <<extra@\textit{name}>>. If |\thesis@extra@|\textit{name} has

% already been defined by the user, |\thesis@def@extra| has no

% effect.

%    \begin{macrocode}

\newcommand{\thesis@def@extra}[2][]{%

  \expandafter\ifx\csname thesis@extra@#2\endcsname\undefined

    \expandafter\def\csname thesis@extra@#2\endcsname{%

      <<extra@\ifx\thesis@empty#1\thesis@empty#2\else#1\fi>>}%

  \expandafter\ifx\csname thesis@extra@#2\endcsname\relax

    \def\thesis@placeholder@extra{<<extra@#2>>}%

    \expandafter\let\csname thesis@placeholder@extra@#2\endcsname

      \thesis@placeholder@extra

    \def\thesis@arg{#1}%

    \ifx\empty\thesis@arg

      \expandafter\let\csname thesis@extra@#2\endcsname

        \thesis@placeholder@extra

    \else

      \expandafter\def\csname thesis@extra@#2\endcsname{#1}%

    \fi

  \fi}

%    \end{macrocode}

% \end{macro}