slightly more standard data merge: Symtax.merge (K true) avoids equality on abstract type Pretty.T and gracefully accepts overriding, Symtab.join prefers first entry as usual;
theory Isar
imports Base
begin
chapter {* Isar language elements *}
text {*
The primary Isar language consists of three main categories of
language elements:
\begin{enumerate}
\item Proof commands
\item Proof methods
\item Attributes
\end{enumerate}
*}
section {* Proof commands *}
text FIXME
section {* Proof methods *}
text FIXME
section {* Attributes *}
text FIXME
end