src/Doc/System/Sessions.thy

     -X NAME      exclude sessions from group NAME and all descendants
     -a           select all sessions
     -b           build heap images
     -c           clean build
     -d DIR       include session directory
+    -f           fresh build
     -g NAME      select session group NAME
     -j INT       maximum number of parallel jobs (default 1)
     -k KEYWORD   check theory sources for conflicts with proposed keywords
     -l           list session source files
     -n           no build -- test dependencies only

   of sessions, as required for other sessions to continue later on.
 
   \<^medskip>
   Option \<^verbatim>\<open>-c\<close> cleans all descendants of the selected sessions before
   performing the specified build operation.
+
+  \<^medskip>
+  Option \<^verbatim>\<open>-f\<close> forces a fresh build of all selected sessions and their
+  requirements.
 
   \<^medskip>
   Option \<^verbatim>\<open>-n\<close> omits the actual build process after the preparatory stage
   (including optional cleanup). Note that the return code always indicates the
   status of the set of selected sessions.