Elements / attributes of the <default_page> element:

<format> Page format. Possible values:
A3, A4, A5, Letter, Legal, ... Sets the page size using the standard page size encodings
C Use a custom page format (Possible alias: c, Cust, CUSTOM). If the custom format has been specified, two other parameters (width and length) must also be indicated in the specified unit of measurement

<orientation> Defines the page orientation. The possibile values are:
P Portrait (vertical). Possible alias: p, Portrait, Vertical, VERTCAL
L Landscape (horizontal). . Possible alias: l, Landscape, h, Horiz, Horizontal

<unit> Specifies the measurement unit for all pages. Possibile values:
mm (millimeters) The default unit and the most commonly used in most applications.
pt (points) One point equals 1/72 of an inch, approximately 0.35 mm. It is the most common unit in typography, often used for character sizes.
cm (centimeters)
in (inches)
The unit of measurement of the page, once defined in this section, cannot be changed and will always be used for the entire report

The page dimensions width and height are normally optional but if you use the "custom" format it is mandatory to specify them in the indicated units of measurement
<width> Page width
<heitght> Page height