code: protected function parse_identifier() {
  		$this->token_start = $this->pos;
  
  		while((++$this->pos < $this->size) && isset($this->identifiers[$this->doc[$this->pos]])) {}
  
  		--$this->pos;
  		return self::TOK_IDENTIFIER;
  	}
docs: Parse identifiers
  @return int Token
  @internal Gets called with {@link $identifiers} characters