src/Doc/JEdit/JEdit.thy

   The Java notation for files needs to be distinguished from the one
   of Isabelle, which uses POSIX notation with forward slashes on
   \emph{all} platforms.\footnote{Isabelle on Windows uses Cygwin
   file-system access.}  Moreover, environment variables from the
   Isabelle process may be used freely, e.g.\ @{file
-  "$ISABELLE_HOME/etc/symbols"} or @{file "$POLYML_HOME/README"}.
+  "$ISABELLE_HOME/etc/symbols"} or @{file_unchecked "$POLYML_HOME/README"}.
   There are special shortcuts: @{file "~"} for @{file "$USER_HOME"}
   and @{file "~~"} for @{file "$ISABELLE_HOME"}.
 
   \medskip Since jEdit happens to support environment variables within
   file specifications as well, it is natural to use similar notation