Reference
Print finishing: binding, folding and what it takes from the page
Everything here happens after the sheets come off the press, and almost all of it constrains decisions made long before that: a page count that has to be a multiple of four, an inner margin wider than the outer one, a panel narrower than its neighbours so the fold closes.
That ordering is the reason to read this early. A finishing constraint designed for is free, and the same constraint discovered on a proof costs a redesign. The page count and the margins are set before anything is printed, and those are the two things every operation below cares about.
Where this API sits: outside it. It renders HTML to PDF, producing a sequence of pages at the size and margins your CSS and the render options set. Imposition, folding and binding happen to paper, so there is no option for any of them and there could not be. What the render decides is how many pages there are and how much room is left at the edges.
Two neighbouring pages live in parts of a document rather than here, because they are about drawing rather than deciding: fold and punch guides and bleed and crop marks. For what the ink does once it is on the sheet, see colour and ink.
Binding
Anything that fastens sheets together takes space from the inner edge and stops the document opening flat. Both of those are margin decisions, and both are made before the design rather than after it.
- Gutter and binding margin
The extra width on the bound edge, which exists because a fastened document does not open flat and the innermost part of the page curves away from the reader.
- Saddle stitch and page count
A booklet made by folding sheets and stapling through the spine, where every sheet carries four pages and the arithmetic is therefore not optional.
- Perfect binding and the spine
Sheets glued at a flat spine rather than folded, which gives a printable spine and a document that opens less flat than a stapled one.
Folding and trimming
A fold is a physical operation on a stack of paper, and paper has thickness. That single fact is behind every surprise in this group.
- Creep and trim
The way inner sheets of a folded booklet push outwards past the outer ones, so trimming the stack flush takes more off the inner pages than the outer.
- Folding schemes and panel widths
A sheet folded into panels, where any panel that folds inside another has to be narrower than it so the fold closes.
- Imposition and reader spreads
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.
Collating, assembling and signing off
What happens between a stack of printed sheets and a finished document somebody can use: the order, the inserts, the fastening, and the moment somebody signs it off.
- Duplex and deliberate blanks
The empty sides that appear in any double-sided document, which are either chosen by you or produced by accident.
- Tab dividers
Divider sheets whose tabs extend beyond the edge of the document, cycling down the page so that every tab is visible at once.
- Stapling and corner clearance
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 and sign-off
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.
On the numbers
Spine width, creep allowance, panel offset and gutter all depend on the stock and the machine, and none of them are constants. No page here quotes one. Every one of them says to get the number from the printer or the binder, because a figure copied from an article is a figure measured on somebody else's paper, and the whole point of these constraints is that they are physical.