separate base plugin for important services that should be always available, despite startup errors of the main plugin;
<?xml version="1.0"?>
<!DOCTYPE SERVICES SYSTEM "services.dtd">
<SERVICES>
<SERVICE NAME="UTF-8-Isabelle" CLASS="org.gjt.sp.jedit.io.Encoding">
new isabelle.jedit_base.Isabelle_Encoding();
</SERVICE>
</SERVICES>