code: def _parseAtCharset(self, src):
          
          if isAtRuleIdent(src, 'charset'):
              src = stripAtRuleIdent(src)
              charset, src = self._getString(src)
              src = src.lstrip()
              if src[:1] != ';':
                  raise self.ParseError('@charset expected a terminating \';\'', src, self.ctxsrc)
              src = src[1:].lstrip()
  
              self.cssBuilder.atCharset(charset)
          return src
docs: [ CHARSET_SYM S* STRING S* ';' ]?