nsITextToSubURI Interface

 Unescapes only non ASCII characters in the given URI fragment 
 note: this method assumes the URI as UTF-8 and fallbacks to the given charset
 in case the data is not UTF-8

 @param aCharset the charset to convert from
 @param aURIFragment the URI (or URI fragment) to unescape
 @return Unescaped aURIFragment  converted to unicode
 @throws NS_ERROR_UCONV_NOCONV when there is no decoder for aCharset
         or error code of nsIUnicodeDecoder in case of conversion failure

AString unEscapeNonAsciiURI(in ACString aCharset, in AUTF8String aURIFragment)

 Unescapes the given URI fragment (for UI purpose only)
 Note: 
 <ul>
  <li> escaping back the result (unescaped string) is not guaranteed to 
       give the original escaped string
  <li> In case of a conversion error, the URI fragment (escaped) is 
       assumed to be in UTF-8 and converted to AString (UTF-16)
  <li> Always succeeeds (callers don't need to do error checking)
 </ul>

 @param aCharset the charset to convert from
 @param aURIFragment the URI (or URI fragment) to unescape
 @return Unescaped aURIFragment  converted to unicode

AString unEscapeURIForUI(in ACString aCharset, in AUTF8String aURIFragment)