class_docstr: A format that stores positions, character start and end, and
  per-position boost information in each posting.
  
  Supports: frequency, weight, positions, position_boosts, characters,
  character_boosts.
class_docstr_tok: ["A","format","that","stores","positions",",","character","start","and","end",",","and","per-position","boost","information","in","each","posting",".","Supports",":","frequency",",","weight",",","positions",",","position_boosts",",","characters",",","character_boosts","."]
code: def decode_character_boosts(self, valuestring):
      if not valuestring.endswith(b(".")):
          valuestring += b(".")
      codes = loads(valuestring[_INT_SIZE + _FLOAT_SIZE :])
      position = 0
      endchar = 0
      posn_char_boosts = []
      for code in codes:
          position = position + code[0]
          startchar = endchar + code[1]
          endchar = startchar + code[2]
          posn_char_boosts.append(
              (position, startchar, endchar, code[3])
          )
      return posn_char_boosts
  
imports: from collections import defaultdict
  from whoosh.analysis import unstopped, entoken
  from whoosh.compat import iteritems, dumps, loads, b
  from whoosh.system import emptybytes
  from whoosh.system import _INT_SIZE, _FLOAT_SIZE
  from whoosh.system import pack_uint, unpack_uint, pack_float, unpack_float
label_desc: Use image node_id 3 for calling the CharacterBoosts obj's underlying member method code with example usage: obj.decode_character_boosts(valuestring) and returns: posn_char_boosts