s-is.  If the string contains non US-ASCII
 characters, it is first character-encoded using the specified
 charset, then transfer-encoded using either the B or Q encoding.
 The resulting bytes are then returned as a Unicode string 
 containing only ASCII characters. <p></div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>word</code> - Unicode string</dd>
<dd><code>charset</code> - the MIME charset</dd>
<dd><code>encoding</code> - the encoding to be used. Currently supported
           