src/Doc/System/Sessions.thy

 \<open>Usage: isabelle build [OPTIONS] [SESSIONS ...]
 
   Options are:
     -B NAME      include session NAME and all descendants
     -D DIR       include session directory and select its sessions
+    -L FILE      append syslog messages to given FILE
     -N           cyclic shuffling of NUMA CPU nodes (performance tuning)
     -P DIR       enable HTML/PDF presentation in directory (":" for default)
     -R           refer to requirements of selected sessions
     -S           soft build: only observe changes of sources, not heap images
     -X NAME      exclude sessions from group NAME and all descendants

   \<^medskip>
   Option \<^verbatim>\<open>-v\<close> increases the general level of verbosity. Option \<^verbatim>\<open>-l\<close> lists
   the source files that contribute to a session.
 
   \<^medskip>
+  Option \<^verbatim>\<open>-L\<close>~\<open>FILE\<close> appends syslog messages to the given file. Such messages
+  can be produced in Isabelle/ML via formal \<^ML>\<open>Output.system_message\<close> or
+  informal \<^ML>\<open>Output.physical_stderr\<close>.
+
+  \<^medskip>
   Option \<^verbatim>\<open>-k\<close> specifies a newly proposed keyword for outer syntax (multiple
   uses allowed). The theory sources are checked for conflicts wrt.\ this
   hypothetical change of syntax, e.g.\ to reveal occurrences of identifiers
   that need to be quoted.
 \<close>