How to expand API for Evo ?

$modx->regClientStartupScript($src);
$modx->regClientCSS( $myCSS );

 // constructor
    function DocumentParser() {
        $this->loadExtension('DBAPI') or die('Could not load DBAPI class.'); // load DBAPI class
        $this->loadExtension('CustomAPI') or die('Could not load CustomAPI class.'); // load CustomAPI class
        $this->dbConfig= & $this->db->config; // alias for backward compatibility
        $this->jscripts= array ();
        $this->sjscripts= array ();
        $this->loadedjscripts= array ();
        // events
        $this->event= new SystemEvent();
        $this->Event= & $this->event; //alias for backward compatibility
        $this->pluginEvent= array ();
        // set track_errors ini variable
        @ ini_set("track_errors", "1"); // enable error tracking in $php_errormsg
    }

    // loads an extension from the extenders folder
    function loadExtension($extname) {
        global $database_type;

        switch ($extname) {
            // Database API
            case 'DBAPI' :
                if (!include_once MODX_BASE_PATH . 'manager/includes/extenders/dbapi.' . $database_type . '.class.inc.php')
                    return false;
                $this->db= new DBAPI;
                return true;
                break;

                // Manager API
            case 'ManagerAPI' :
                if (!include_once MODX_BASE_PATH . 'manager/includes/extenders/manager.api.class.inc.php')
                    return false;
                $this->manager= new ManagerAPI;
                return true;
                break;
                
                // CustomAPI
            case 'CustomAPI' :
                if (!include_once MODX_BASE_PATH . 'manager/includes/extenders/custom.api.class.inc.php')
                    return false;
                $this->custom= new CustomAPI;
                return true;
                break;

            default :
                return false;
        }
    }

<?php
class CustomAPI {
	var $customId; 
	var $customClass;
	var $customLink;
	var $customQuery;
	var $customQueryValue;
			
		function setCustomClass($customClass) {
		$this->customClass = $customClass ? $customClass : 'my-class';
		return ' class="'.$this->customClass.'" ';
		}

		function setCustomQuery($customQuery) {
		$this->customQuery = $customQuery ? $customQuery : 'searching';
		return $this->customQuery;
		}
		
		function setCustomQueryValue($customQueryValue) {
		$this->customQueryValue = $customQueryValue ? $customQueryValue : 'something';
		return '='.$this->customQueryValue;
		}
	
		function setCustomId($customId,$customQuery,$customQueryValue){
		global $modx;
		$this->customId = $customId ? $customId : 1;
		$url = $modx->makeUrl($this->customId,'',$this->setCustomQuery($customQuery) . $this->setCustomQueryValue($customQueryValue), 'full');
		return ' href="'.$url.'"';
		}
	
		function setCustomLink($customLink){
		$this->customLink = $customLink ? $customLink : 'link text here';
		return $this->customLink;
		}
		
		function setCustomOutput($customClass,$customId,$customLink,$customQuery,$customQueryValue) {
		$o .= '<a';
		$o .= $this->setCustomId($customId,$customQuery,$customQueryValue);
		$o .= $this->setCustomClass($customClass);
		$o .= '>';
		$o .= $this->setCustomLink($customLink);
		$o .= '</a>';
		return $o;
	}
	
}
?>

<?php
/*
$text = $modx->custom->setCustomOutput('link class name', 'document id', 'link text', 'querystring name', 'querystring value');
defaults set in cusom api class are => ('my-class', '1', 'link text here', 'searching', 'something');
gives output of <a href="http://localhost/development/index.html?searching=something" class="my-class">link text here</a>
*/
$text = $modx->custom->setCustomOutput('','' ,'','','');
return $text;
?>