$TCA['tt_content']['types']['list']['subtypes_addlist'][$_EXTKEY.'_pi1'] ='pi_flexform';
t3lib_extMgm::addPiFlexFormValue($_EXTKEY.'_pi1', 'FILE:EXT:'.$_EXTKEY . '/flexform_ds_pi1.xml');

$extensionName = t3lib_div::underscoredToUpperCamelCase($_EXTKEY);
$pluginSignature = strtolower($extensionName) . '_pi1';  
$TCA['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 'pi_flexform';
t3lib_extMgm::addPiFlexFormValue($pluginSignature, 'FILE:EXT:'.$_EXTKEY.'/Configuration/Flexforms/flexform_list.xml');    

<T3DataStructure>
    <sheets>
        <sheet1>
            <ROOT>
                <TCEforms>
                    <sheetTitle>Code</sheetTitle>
                </TCEforms>
                <type>array</type>
                <el>
                    *** Elemente ***
                </el>
            </ROOT>
        </sheet1>
        <sheet2>
            <ROOT>
                <TCEforms>
                    <sheetTitle>Settings</sheetTitle>
                </TCEforms>
                <type>array</type>
                <el>
                    *** Elemente ***
                </el>
            </ROOT>
        </sheet2>		
    </sheets>
</T3DataStructure>

  <codesnipet>
    <TCEforms>
      <label>Code Snipet</label>
      <config>
        <type>text</type>
        <cols>30</cols>
        <rows>20</rows>
       </config>
     </TCEforms>
   </codesnipet>

<language>
    <TCEforms>
        <label>Language</label>
		<config>
		 <type>select</type>
		 <items type="array">
		   <numIndex index="0" type="array">
		    <numIndex index="0">Plain</numIndex>
		    <numIndex index="1">plain</numIndex>
		   </numIndex>
		   <numIndex index="1" type="array">
		    <numIndex index="0">Bash</numIndex>
		    <numIndex index="1">bash</numIndex>
		    </numIndex>
		   <numIndex index="2" type="array">
		    <numIndex index="0">Cpp</numIndex>
		    <numIndex index="1">cpp</numIndex>
		   </numIndex>
		   <numIndex index="3" type="array">
		    <numIndex index="0">C-Sharp</numIndex>
		    <numIndex index="1">csharp</numIndex>
		   </numIndex>					   
		  </items>
		</config>
    </TCEforms>
</language>

<language>
    <TCEforms>
        <label>Language</label>
		<config>
			<type>select</type>
			<foreign_table>my_table</foreign_table>
			<minitems>1</minitems>
			<maxitems>10</maxitems>
			<multiple>1</multiple>
			<size>5</size>
			<autoSizeMax>10</autoSizeMax>
			<itemListStyle>Width:250px</itemListStyle>
		</config>
    </TCEforms>
</language>

/**
 * initializes the flexform and all config options ;-)
 */
function init(){
    $this->pi_initPIflexForm(); // Init and get the flexform data of the plugin
    $this->lConf = array(); // Setup our storage array...
    // Assign the flexform data to a local variable for easier access
    $piFlexForm = $this->cObj->data['pi_flexform'];

    // Traverse the entire array based on the language...
    // and assign each configuration option to $this->lConf array...
    foreach ( $piFlexForm['data'] as $sheet => $data ) {
        foreach ( $data as $lang => $value ) {
            foreach ( $value as $key => $val ) {
                $this->lConf[$key] = $this->pi_getFFvalue($piFlexForm, $key, $sheet);
            }
        }
    }
}
		
/**
* The main method of the PlugIn
*
* @param string  $content: The PlugIn content
* @param array  $conf: The PlugIn configuration
* @return The content that is displayed on the website
*/
function main($content, $conf) {
	$this->conf = $conf;
	$this->pi_setPiVarDefaults();
	$this->pi_loadLL();
	 
	$this->init();
	$content = $this->lConf['codesnipet'];
	 
	return $this->pi_wrapInBaseClass($content);
}