freepascal.compiler/docs/syntax/external.syn

\begin{psyntax}{External directive}{externaldirective}
\synt{external\ directive}
\lit*{external}
\[
  \synt{string\ constant}
  \[
    \lit*{name} \synt{string\ constant}\\
    \lit*{index} \synt{integer\ constant}
  \]
\]
\end{psyntax}