code: def add_chars(self, chars):
          'Add given chars to char set'
          for c in chars:
              if self._ignorecase:
                  self._whitelist_chars.add(c.lower())
                  self._whitelist_chars.add(c.upper())
              else:
                  self._whitelist_chars.add(cf add_chars(self, chars):
          'Add given chars to char set'
          for c in chars:
              if self._ignorecase:
                  self._whitelist_chars.add(c.lower())
                  self._whitelist_chars.add(c.upper())
              else:
                  self._whitelist_chars.add(c)
docs: Add given chars to char set