code: function OpenXML_CTypesPrepareExt($FileOrExt, $ct='') {
  
  		$ext = $this->Misc_FileExt($FileOrExt);
  
  		$this->OpenXML_CTypesInit();
  		
  		$lst =& $this->OpenXmlCTypes['Extension'];
  		if (isset($lst[$ext]) && ($lst[$ext]!=='') ) return;
  
  		if (($ct==='') && isset($this->ExtInfo['pic_ext'][$ext])) $ct = 'image/'.$this->ExtInfo['pic_ext'][$ext];
  
  		$lst[$ext] = $ct;
  
  	}
docs: Prepare information for adding a content type for an extension.
  It needs to be completed when a new picture file extension is added in the document.