The stylesheet pretext-latex.xsl can produce two very similar outputs. Each is a file in syntax, which can be converted to a PDF with a executable (“engine”). However, there are two purposes for such a PDF. The first is a document which is meant to be read on a screen. We call this an electronic PDF. The second is meant to be printed as a physical book, so it would be the file you provide to a copy shop, campus bookstore, or print-on-demand service (see Chapter 41). We call this a print PDF. So as you read this, keep in mind that the conversion is really two-converters-in-one.
The publisher file entry latex/@print controls the selection of the two output modes of this single stylesheet. The default is no for the electronic version, and yes will change to the print version. See Subsection 40.3.1 for the specifics of this entry.