class_docstr: Helper object that allows to configure `characters` strategy with
  various unicode categories and characters. Also allows negation of
  configured set.
  
  :param negate: If True, configure :func:`hypothesis.strategies.characters`
      to match anything other than configured character set
  :param flags: Regex flags. They affect how and which characters are matched
docstr: Add given char to the whitelist.
docstr_tok: ["Add","given","char","to","the","whitelist","."]
code: def add_char(self, char):
      """Add given char to the whitelist."""
      c = self.code_to_char(char)
      self._whitelist_chars.add(c)
      if (
          self._ignorecase
          and re.match(re.escape(c), c.swapcase(), flags=re.IGNORECASE)
          is not None
      ):
          self._whitelist_chars.add(c.swapcase())
  
imports: from __future__ import absolute_import, division, print_function
  import operator
  import re
  import sre_constants
  import sre_parse
  import sys
  import hypothesis.strategies
  from hypothesis import reject
  from hypothesis.internal.charmap import as_general_categories, categories
  from hypothesis.internal.compat import PY3, hrange, hunichr, int_to_byte, text_type
label_desc: Use image node_id 4 for calling the CharactersBuilder obj's underlying member method code with example usage: obj.add_char(char) without return types