The MARGINS line specifies the default margins. The first number specifies the margin type, which is the same as the MTYP in the DEVMODE structure. The example in the Header section shows that 1 represents one inch. The next eight numbers are the actual margins in the following order: top, left, right, bottom.
Each margin is represented by a pair of numbers. The first number is the integer part and the second number is the fractional part. In the example above, all the margins are 0.5 inches.
You can specify the optional MIRROR keyword after the margins, separated by a comma. This keyword indicates that the page format must have mirrored margins. In this case, the user-specified mirror margins setting is ignored.