13. The unit as recited in claim 12 wherein said peripheral unit is initially interpreting said second control language instead of said first control language, said unit comprising: means responsive to a next command not being an end of job marker, but being an escape character, and further responsive to the peripheral unit operating in other than a binary mode of communication, to pass said command and following data to said parse means for determining whether a language boundary has been encountered.
12. In a peripheral unit for creating marked pages, said peripheral unit adapted to receive, interpret and respond to a plurality of control languages that may appear in an input data stream, a system for identifying occurrence of a language boundary between a first control language and a second control language, said language boundary indicating a cessation of commands configured in accord with said first control language and a commencement of commands configured in accord with said second control language, the peripheral unit comprising: first means for determining if a newly received command in said data stream requires a printing of an initial mark on a page; and parse means responsive to a determination from said first means that said newly received command requires a printing of said initial mark on said page, for determining if said newly received command and a portion of said input data stream are indicative of a language boundary.