| SAXONICA | 
saxon:string-to-base64Binary($in as xs:string, $encoding as xs:string) ==> xs:base64Binary
This function takes as input a string and the name of a character
            encoding (for example "UTF8"). It encodes the contents of the string value as a sequence of bytes
            using a particular encoding, and returns the xs:base64Binary representation
            of this sequence of bytes.
         
For example, the call saxon:string-to-base64Binary("Dassel", "UTF8") returns the
            xs:base64Binary value  whose lexical representation is "RGFzc2VsIA==".