checkAttribute( "from", this.from );
checkStringAttribute( "from", this.from );
    public void doTag(XMLOutput output) throws Exception    {        Process process = getCurrentProcess();        checkAttribute( "from",                        this.from );        checkAttribute( "to",                        this.to );        State fromState = process.getState( this.from );        if ( fromState == null )        {            throw new JellyException( "No such state \"" + this.from  + "\"" );        }        State toState = process.getState( this.to );        if ( toState == null )        {            throw new JellyException( "No such state \"" + this.to  + "\"" );        }        this.transition = fromState.addTransition( toState,                                                   this.description );        invokeBody( output );    }