def char_groups(self, t, i):
        """Handle character groups."""

        current = []
        pos = i.index - 1
        found = 0
        sub_first = None
        escaped = False
        first = None

        try:
            while True:
                if not escaped and t == "\\":
                    escaped = True
                elif escaped:
                    escaped = False
                    current.extend(self.reference(t, i, True))
                elif t == "[" and not found:
                    found += 1
                    first = pos
                    current.append(t)
                elif t == "[" and found and self.version == _regex.V1:
                    # Start of sub char set found
                    posix = None if self.is_bytes else self.get_posix(i)
                    if posix:
                        current.append(posix)
                        pos = i.index - 2
                    else:
                        found += 1
                        sub_first = pos
                        current.append(t)
                elif t == "[":
                    posix = None if self.is_bytes else self.get_posix(i)
                    if posix:
                        current.append(posix)
                        pos = i.index - 2
                    else:
                        current.append(t)
                elif t == "^" and found == 1 and (pos == first + 1):
                    # Found ^ at start of first char set; adjust 1st char position
                    current.append(t)
                    first = pos
                elif self.version == _regex.V1 and t == "^" and found > 1 and (pos == sub_first + 1):
                    # Found ^ at start of sub char set; adjust 1st char sub position
                    current.append(t)
                    sub_first = pos
                elif t == "]" and found == 1 and (pos != first + 1):
                    # First char set closed; log range
                    current.append(t)
                    found = 0
                    break
                elif self.version == _regex.V1 and t == "]" and found > 1 and (pos != sub_first + 1):
                    # Sub char set closed; decrement depth counter
                    found -= 1
                    current.append(t)
                else:
                    current.append(t)
                pos += 1
                t = next(i)
        except StopIteration:
            pass

        if escaped:
            current.append(t)
        return current
Handle character groups.