label->idf relationship, note that this means that labels can be used only once
        $this->destinations["$label"] = $id;
    }

    /**
     * define font families, this is used to initialize the font families for the default fonts
     * and for the user to add new ones for their fonts. The default bahavious can be overridden should
     * that be desired.
     *
     * @param $family
     * @param string $options
     */
    function setFontFamily($family, $options = '')
    {
        if (!is_array($options)) {
            if ($family === 'init') {
                // set the known family groups
                // these font families will be used to enable bold and italic markers to be included
                // within text streams. html forms will be used... <b></b> <i></i>
                $this->fontFamilies['Helvetica.afm'] =
                    [
                        'b'  => 'Helvetica-Bold.afm',
                        'i'  => 'Helvetica-Oblique.afm',
                        'bi' => 'Helvetica-BoldOblique.afm',
                        'ib' => 'Helvetica-BoldOblique.afm'
                    ];

                $this->fontFamilies['Courier.afm'] =
                    [
                        'b'  => 'Courier-Bold.afm',
                        'i'  => 'Courier-Oblique.afm',
                        'bi' => 'Courier-BoldOblique.afm',
                        'ib' => 'Courier-BoldOblique.afm'
                    ];

                $this->fontFamilies['Times-Roman.afm'] =
                    [
                        'b'  => 'Times-Bold.afm',
                        'i'  => 'Times-Italic.afm',
                        'bi' => 'Times-BoldItalic.afm',
                        'ib' => 'Times-BoldItalic.afm'
                    ];
            }
        } else {

            // the user is trying to set a font family
            // note that this can also be used to set the base ones to something else
            if (mb_strlen($family)) {
                $this->fontFamilies[$family] = $options;
            }
        }
    }

    /**
     * used to add messages for use in debugging
     *
     * @param $message
     */
    function addMessage($message)
    {
        $this->messages .= $message . "\n";
    }

    /**
     * a few functions which should allow the document to be treated transactionally.
     *
     * @param $action
     */
    function transaction($action)
    {
        switch ($action) {
            case 'start':
                // store all the data away into the checkpoint variable
                $data = get_object_vars($this);
                $this->checkpoint = $data;
                unset($data);
                break;

            case 'commit':
                if (is_array($this->checkpoint) && isset($this->checkpoint['checkpoint'])) {
                    $tmp = $this->checkpoint['checkpoint'];
                    $this->checkpoint = $tmp;
                    unset($tmp);
                } else {
                    $this->checkpoint = '';
                }
                break;

            case 'rewind':
                // do not destroy the current checkpoint, but move us back to the state then, so that we can try again
                if (is_array($this->checkpoint)) {
                    // can only abort if were inside a checkpoint
                    $tmp = $this->checkpoint;

                    foreach ($tmp as $k => $v) {
                        if ($k !== 'checkpoint') {
                            $this->$k = $v;
                        }
                    }
                    unset($tmp);
                }
                break;

            case 'abort':
                if (is_array($this->checkpoint)) {
                    // can only abort if were inside a checkpoint
                    $tmp = $this->checkpoint;
                    foreach ($tmp as $k => $v) {
                        $this->$k = $v;
                    }
                    unset($tmp);
                }
                break;
        }
    }
}