3.1.1 The Syntax Format In the description of the built-in functions, the syntax of each one is listed. For each of the syntax diagrams, the parts written in italic font names the parameters. Terms enclosed in [square brackets] denote optional elements. And the courier font is used to denote that something should be written as is, and it is also used to mark output from the computer. Note that in standard REXX it is not really allowed to let the last possible parameter be empty if all commas are included, although some implementations allow it. In the following calls: say D2X( 61 ) say D2X( 61, 1 ) say D2X( 61, ) The two first return the string consisting of a single character A, while the last should return error. If the last argument of a function call is omitted, you can not safely include the immediately preceding comma.