Print finishing / Collating, assembling and signing off
Blank pages in a double-sided document, and making them deliberate
The empty sides that appear in any double-sided document, which are either chosen by you or produced by accident.
What is physically going on
A double-sided document has two sides per sheet whether or not you have content for both. Every section that has to start on a right-hand page will sometimes leave the preceding left-hand side empty, and a document with an odd final page count ends with an empty back. Those blanks are unavoidable and unremarkable. What makes them a defect is when they are unmarked and unexpected: a reader who turns to a blank page in the middle of a report has no way to know whether it is deliberate or whether their copy failed to print, and in a controlled document that question has to be answerable.
The decisions
Reasons rather than a description of the code. Where a number depends on the stock or the press, the instruction is to get it from the printer rather than to quote one here, because spine width, creep and bulk are not constants.
- Use the right-hand break rather than a plain page break for anything that must start recto, and let the blank be inserted for you.
- Style the inserted blank with the blank page rule so it carries no running header and no folio, otherwise it does not look blank.
- Mark blanks as intentionally blank in a formal or controlled document, where a reader has to be able to tell a blank from a printing failure.
- Count the blanks into the total, because they are pages: they are numbered, they are printed, and they affect any binding that needs a particular multiple.
- Do not fill a blank with decoration to avoid the question. A half-hearted graphic reads as filler and makes the document look padded.
- Check the final page. A document that ends on a right-hand page leaves the back of that sheet blank, which is where a back cover belongs.
What it means for the page rule
The page rule is the part of this a document author controls. The binder decides the gutter and the printer decides the creep allowance; the document's job is to leave the room those decisions need.
/* Recto starts, with the blank inserted for you rather than by hand. */
.part { break-before: right; }
/* The inserted leaf still gets the body page rule unless you empty it,
so a blank page with a running header on it is the usual failure. */
@page :blank {
@top-left { content: ""; }
@top-center { content: ""; }
@bottom-left { content: ""; }
@bottom-right { content: ""; }
}
/* In a controlled document, say so, so a reader can tell a deliberate
blank from a page that failed to print. */
.intentionally-blank::after {
content: "This page is intentionally blank";
font-size: 8pt;
letter-spacing: 0.12em;
text-transform: uppercase;
color: #999;
}What people do instead
Forcing the parity with an empty element and a page break. The resulting page is part of the flow, so it takes the body page rule and prints a header and a folio, and a blank page with furniture on it looks like a page whose content went missing.
How to find out rather than assume
Render a document where a section falls on an even boundary and one where it falls on an odd one. Both should start recto, one of them preceded by a genuinely empty leaf with nothing printed on it at all. Then confirm the page numbering did not skip.
Where this API sits in it
Outside it. This API renders HTML to PDF: it produces a sequence of pages at the size and margins your CSS and the render options set, and everything on this page happens afterwards, to paper, in a bindery. There is no imposition option, no binding option and no finishing option, and there could not be, because none of those are properties of a file. What the render does decide is the two things finishing cares about most: how many pages there are, and how much room is left at the edges. Both of those are set before anything is printed, which is why a finishing constraint discovered late is expensive and one designed for is free.
Frequently asked
Can the API impose the pages into printer spreads?
No, and you should not want it to. Imposition is done by the printer with tooling built for it, against the specific press, stock and folding scheme, and the input that tooling wants is single pages in reading order, which is what a render naturally produces. Supplying anything else means somebody has to undo it first.
How do I get the page count to a multiple of four?
By deciding where the padding goes rather than letting it land at the end. Add the blanks deliberately, style them with the blank page rule so they carry no folio or running header, and mark them as intentionally blank if the document is formal. Counting the covers into the total is the step people miss.
Do any of these apply to a document that is only ever read on screen?
No. This cluster is about physical operations on paper, so if a document is genuinely never printed, none of it is your problem. It is worth checking that assumption rather than making it: delivery notes, permits, method statements and invoices all end up on paper more often than the people generating them expect.
Related finishing topics
The operations that constrain each other, then the rest of the same group.
Why a stapled booklet has to have a page count divisible by four
A booklet made by folding sheets and stapling through the spine, where every sheet carries four pages and the arithmetic is therefore not optional.
Supplying single pages, and letting the printer impose them
The rearrangement of pages into the order they have to be printed on a sheet, which is the printer's job and is made harder by supplying pages already paired.
Tab dividers in a printed manual, and where the tabs actually sit
Divider sheets whose tabs extend beyond the edge of the document, cycling down the page so that every tab is visible at once.
Corner stapling, and the content the staple goes through
A single staple through the top corner, which is how most office documents are fastened and which occupies a specific area of every page.
Proofing a document on the stock and device it will actually use
The check before a run, which is only worth anything if it is done on the material and the machine the real thing will use.
Section divider page, as a layout problem
The block in the document that this constraint lands on.
Every finishing topic
The full list, grouped by binding, folding and trimming, and collation.
None of this is a render option, and none of it could be. What the render controls is that the page count and the margins are the ones the finishing needs.