Xerox Escape Sequence

Xerox Escape Sequence or XES is a page [description language] developed by Xerox corporation and introduced with their 2700 laser printers in 1982. XES offers similar capabilities to Hewlett-Packard's Printer Command Language, which first appeared in 1984. XES is supported by most Xerox laser printers including the 2700. 3700, 4011, 4030, 4045, 4197, 4213, 4235, and 4700.
XES is sometimes known as UDK, from User Defined Key, the character which introduces the printer command. Commands are normally introduced by the escape character. This character may be changed in the data stream by the command =UDK=c, where c is the value to be used going forward. c may be any character except U, D, K, space, or 0 through 9.