[css-page] positioning of crop marks

Crop marks have several properties:

[1] mark offset is the distance from the edge of the page box to the start of the mark.
[2] the length of the mark itself
[3] the distance from the end of the mark to the edge of the PDF (I'll use "PDF" as a shorthand for the end result of creating a paged rendition).

I don't think it makes sense to set [3] directly in CSS. There's no precedent for doing this in InDesign or Quark, and I've never seen any guidelines that refer to this measurement. Guidelines always mention [1], and sometimes give explicit instructions on how much the PDF extends beyond the page boundary. So I think the more useful set of properties is:

[1] mark offset
[2] mark length
[3] distance from edge of page box to edge of PDF.

Antenna House and Prince handle this in different ways. Prince has a "prince-trim" property, where the sum of the bleed and trim amounts gives the distance from the page box to the edge of the PDF.  Unfortunately Prince 9 seems to fix the mark offset at 9pts, regardless of other settings (it was indirectly adjustable in earlier versions).

Antenna House describes this using crop properties (there's a link to http://www.w3.org/TR/2003/WD-css3-content-20030514/#the-crop in their doc, which seems weird to me).

-ah-crop-offset is the distance from the page box to the the edge of the PDF. So there's a mismatch here:

prince-bleed + prince-trim = -ah-crop-offset

Antenna House also has:

 -ah-printer-marks-zero-margin

which is what I would call the marks offset, but it only works in the case where there's zero bleed. I suspect that if there is bleed, AH sets the mark offset to the bleed value, which doesn't meet some of my use cases. AH also has:

-ah-printer-marks-line-length
-ah-printer-marks-line-color
-ah-printer-marks-line-width

The first is useful, but I might want to wait for level 4 for the last two :)

* * *

So, I would propose adding three properties to css3-page, in addition to bleed and marks:

Name: mark-offset
Value: length
Initial: 12pt
Applies to: page context
Inherited: no
Media: visual, paged
Computed value: as specified
Percentages: refer to width of page box

Name: mark-length
Value: length
Initial: 24pt
Applies to: page context
Inherited: no
Media: visual, paged
Computed value: as specified
Percentages: refer to width of page box

Name: trim
Value: length {1..4} [both Prince and AH allow this to be specified differently on each side of the page]
Initial: ??? [ideally the default would be zero if no marks or bleeds, equal to the bleed if there's bleed but no marks, and 36pt if there's marks]
Applies to: page context
Inherited: no
Media: visual, paged
Computed value: as specified
Percentages: refer to width of page box

With these properties, the user can control the amount of bleed, the positioning of the crop marks, and the total extent of the page.

AH has all these properties, but with different names, and I'd hope the marks offset would be independent of bleed. Prince has the trim property, but with a different definition, and would need the others.

I suppose we could survive negative lengths on these. A negative mark-offset would extent the crop marks into the page areas. Negative trim would essentially crop the page. A negative mark-length would cause the universe to destabilize.

* * *

Some examples of common usage:

[1] Self-published author using lulu.com. For a book with bleeds with a finished size of 6" x 9", we would set:

@page {
size: 6in 9in;
marks: none;
bleed: .125in;
trim: .125in /* this bothers me a bit; if there's no marks should trim default to the bleed amount? */
}

The resulting PDF will be 6.25in by 9.25in.

[2] Major publisher sends same book to R.R. Donnelly:

@page {
size: 6in 9in;
marks: crop cross;
bleed: 13.5pt;
mark-offset: 30pt;
mark-length: 15pt;
trim: 45pt;
}

The resulting PDF will be 7.25in x 10.25in

[3] Major publisher sends same book to Quebecor:

@page {
size: 6in 9in;
marks: crop cross;
bleed: 9pt;
mark-offset: 12pt; /*given that default with marks is 36pt*/
}

The resulting PDF will be 7in x 10in

[4] Normal citizen makes PDF for printing at home

@page {
size: letter;
}

The resulting PDF is 8.5in x 11in

* * *

Thoughts? I've started a thread on the Prince forum asking about some of these issues, but am reluctant to copy AH and Prince on this without some feedback from the spec editors and WG.

Thanks,

Dave

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