The Publisher sets internal variables that can be used in the layout rules. These variables always begin with an underscore, so your own variables should not have the underscore as the first character. Otherwise there could be collisions when assigning names.
The value of the bleed.
The value specified on the command line.
The last value (
data="…") in a table line. See section Headers and footers with running sum.
The pass in a `<Loop>' loop.
The mode for the pass. Separated by commas.
The width and height of the page. Default is 210mm and 297mm.
The name of the text area of the whole page.
Also worth mentioning:
Image files included in the Publisher. Can be used for testing purposes.