write_base64
Description:
Writes value of length len, encoded to base64, as content of the current element.
Parameters:
| this | 
           an XmlDocument  | 
      
| value | 
           value to write as the content  | 
      
| len | 
           length of   | 
      
Writes value of length len, encoded to base64, as content of the current element.
| this | 
           an XmlDocument  | 
      
| value | 
           value to write as the content  | 
      
| len | 
           length of   |