The regular expression used to parse integer or decimal numbers.
private const PARSE_REGEXP_NUMERICAL = '/^' . '(?<sign>[\\-\\+])?' . '(?<integral>[0-9]+)?' . '(?<point>\\.)?' . '(?<fractional>[0-9]+)?' . '(?:[eE](?<exponent>[\\-\\+]?[0-9]+))?' . '$/';