The decimal mark is used to separate the integer from the fractional part of non-integer numbers. The optional nature of the UNA segment and the initial choice of the comma (",") as the default decimal mark provide a source of common confusion. Versions 1 through 3 of the ISO 9735 syntax rules specify the comma as the default; version 4 states that the decimal mark position in the UNA segment is to be ignored and that the comma and the dot (".") may be used indifferently in numeric data values. The UNB segment indicates which version of the syntax rules is in effect.