manual: Further rewrite :session doc.

* doc/org.texi (session): Spruce up.

doc/org.texi

@@ -15570,20 +15570,23 @@ execution.
 @subsubsection @code{:session}
 @cindex @code{:session}, src header argument
 
-The @code{:session} header argument starts a (possibly named) session for an interpreted
-language where state is preserved.  All code blocks sharing the same name are exectuted by the same interpreter process.  By default, a session is not started.
+The @code{:session} header argument starts a (possibly named) session for an
+interpreted language where the interpreter’s state is preserved.  All code
+blocks sharing the same name are exectuted by the same interpreter process.
+By default, a session is not started.
 
 @itemize @bullet
 @item @code{none}
-The default.  Each block is evaluated in its own session.  The session is
-not preserved after the evaluation.
+The default.  Each block is evaluated in its own interpreter process, which
+is terminated after the evaluation.
 @item @code{other}
 Any other string passed to the @code{:session} header argument will give the
-session a name.  If the given name is empty, the session is named according
-to the language used in the block.  All blocks with the same session name
-share the same session.  Using different session name enables concurrent
-sessions (even for the same interpreted language).  E.g., @code{:session
-mysession}.
+session a name.  For example, @code{:session mysession}.  If @code{:session}
+is given but no name string is specified, the session is named according to
+the language used in the block.  All blocks with the same session name share
+the same session.  Using different session names enables concurrent sessions
+(even for the same interpreted language).
+
 @end itemize
 
 @node noweb