@Section
    @Title { Page margins, page boxes, and page backgrounds }
    @Tag { margins }
@Begin
@PP
There are six options for setting the top and bottom margins on each
margin.options @RawIndex { margin options }
margin.options.in.pages @SubIndex { in pages }
top.margin @Index @Code "@TopMargin"
foot.margin @Index @Code "@FootMargin"
odd.left.margin @Index @Code "@OddLeftMargin"
odd.right.margin @Index @Code "@OddRightMargin"
even.left.margin @Index @Code "@EvenLeftMargin"
even.right.margin @Index @Code "@EvenRightMargin"
page, and the left and right margins on odd and even pages.  Here they
are with their default values:
@ID @OneRow @Code @Verbatim {
@TopMargin { 2.50c }
@FootMargin { 2.50c }
@OddLeftMargin { 2.50c }
@OddRightMargin { 2.50c }
@EvenLeftMargin { 2.50c }
@EvenRightMargin { 2.50c }
}
When setting these options you must ensure that
@ID @Math { @Code "@OddLeftMargin" + @Code "@OddRightMargin" =
@Code "@EvenLeftMargin" + @Code "@EvenRightMargin" }
In other words, the total margin on odd pages must be the same as on
even pages.
@PP
In addition, four options are provided which add extra left and right
margins to the page @I body (that is, everything but the running headers
and footers):
@ID @OneRow @Code @Verbatim {
@OddLeftBodyMargin { 0c }
@OddRightBodyMargin { 0c }
@EvenLeftBodyMargin { 0c }
@EvenRightBodyMargin { 0c }
}
The default is to add no page body margins, as shown.  Most people who
use page body margins would change only @Code "@OddRightBodyMargin" and
{@Code "@EvenLeftBodyMargin"}, since those are the outside margins.  As
for ordinary margins, the total (left plus right) page body margin must
be the same on odd and even pages.  Margin notes
(Section {@NumberOf marginnotes}) occupy body margin space.
@PP
You can draw a box around each page.  The relevant options and their
default values are
@ID @OneRow @Code @Verbatim {
@PageBoxType { None }
@PageBoxMargin { 1.00c }
@PageBoxLineWidth {}
@PageBoxPaint { None }
@PageBoxShadow { 0.06c }
}
You get boxes by changing the @Code "@PageBoxType" option:
page.box.type @Index @Code "@PageBoxType"
@ID @OneRow @Tab
    @Fmta { @Col @Code A ! @Col @CC B }
{
@Rowa
    A { "@PageBoxType { None }" }
    B { (no box) }
@Rowa
@Rowa
    A { "@PageBoxType { Box }" }
    B { @Box 1.0c @Wide 1.4c @High }
@Rowa
@Rowa
    A { "@PageBoxType { CurveBox }" }
    B { @CurveBox 1.0c @Wide 1.4c @High }
@Rowa
@Rowa
    A { "@PageBoxType { ShadowBox }" }
    B { @ShadowBox 1.0c @Wide 1.4c @High }
}
Page boxes reduce the amount of space available to the page contents,
so your columns will become somewhat narrower and shorter when you
introduce them.
@PP
The {@Code "@PageBoxMargin"}, {@Code "@PageBoxLineWidth"},
{@Code "@PageBoxPaint"}, and {@Code "@PageBoxShadow"} options affect
the page box exactly as the {@Code margin}, {@Code linewidth},
{@Code paint}, and {@Code shadow} options described
for other boxes in Section {@NumberOf boxes} do.  For example,
@ID @OneRow @Code @Verbatim {
@PageBoxType { CurveBox }
@PageBoxMargin { 1.0c }
@PageBoxPaint { grey }
}
draws a curved box, painted grey, around each page, with a one
centimetre margin between its boundary and the page contents.  If the
left margin is 2.5 centimetres, say, this gives a total left margin
from the page edge to the page contents of 3.5 centimetres.
@PP
More generally, you can enclose each page in any object at all,
using @Code "@PageEnclose":
@ID @Code {
"@PageEnclose { @Body }"
}
Within the @Code "@PageEnclose" option, @Code "@Body" stands for the
page, and it must occur exactly once.  You could place a curved box
around each page, for example, by writing
@ID @Code {
"@PageEnclose { @CurveBox @Body }"
}
This could be done with {@Code "@PageBox"}, but @Code "@PageEnclose"
offers infinitely many possibilities.
@PP
@Code "@PageBackground" replaces the usual white background of the page:
page.background @Index @Code "@PageBackground"
@ID @Code {
"@PageBackground { @Scale 60d @Rotate lightgrey @Colour DRAFT }"
}
Its value is an object which is drawn on each page, within the
margins, before the page contents are drawn.  This example draws
a large word DRAFT in light grey diagonally across each page:
@ID @Box margin { 0c } 0.2 @Scale @IncludeGraphic draft.eps
You have to find a suitable angle by experiment.  As Section
{@NumberOf scaling} explains, @Code "@Scale" with no scale factor
only takes account of the available horizontal space, not the
available vertical space, so if your angle is too steep the result
will be too tall for the page and you will get a regrettably obscure
warning message about a `broken size constraint.'  The solution is
to try a smaller angle.
@PP
Another useful page background draws marks to show where the margins
boundarymarks @Index @Code "@BoundaryMarks"
cut.marks @Index { cut marks }
lie:
@ID @Code "@PageBackground { @BoundaryMarks }"
produces something like this around each page:
@DP @DP
@ID { |@DisplayIndent 3c @High 2c @Wide @HExpand @VExpand @BoundaryMarks }
@DP @DP
The @Code "@BoundaryMarks" symbol has options for controlling the
line width (thickness), the line length, and the gap between the
ends of the lines and the corner of the text area:
@ID @OneRow @Code @Verbatim {
@PageBackground {
    @BoundaryMarks
        linewidth { 0.2p }
        length { 0.5c }
        gap { 0.5c }
}
}
This shows the default values:  0.2 points for line width,
0.5 centimetres for the others.
@End @Section
