When each applies

Each companion format is a slice of a document, cut out for a job the whole document is too heavy for.

In short A snippet appears when someone reuses a piece of a layout in another document. A library appears when that reuse becomes a habit. An InCopy story appears when writing and layout are separate jobs, and an assignment when that split involves several editors. In every case the design map, the part that makes a set of parts into one document, is what the slice leaves behind.

The workflows

• Reusing a piece of layout. A designer exports or drags a group of page items out as an .idms file and places it into another document later. The snippet carries the styles and colours its items use, so they keep their formatting wherever they land.
• Keeping a shelf of reusable items. A library (.indl) holds items a team uses across many documents: a masthead, a pull-quote treatment, a logo lockup.
• Editing copy apart from layout. The layout stays in the InDesign document; the text of a story goes out as an .icml file to an editor working in InCopy and comes back, without anyone opening the layout.
• Sharing a document among editors. An .icma assignment groups stories into a unit of work so that several editors can work on one layout at the same time without editing the same text.

How each relates to the package

Read against a package, each format keeps one layer of what the package holds:

• a snippet is page items lifted off their spread, with just enough resources to stand up again elsewhere;
• an InCopy story is one entry of the design map's StoryList on its own: text, without the frames on spreads that give it a place;
• an assignment is a list about stories rather than the stories themselves.

What all three lack is the design map: the part that names the spreads, lists the stories and holds the document-wide settings — layers, sections, text variables, conditions, hyperlinks (see package anatomy). Without it there is no document to assemble, only material for one.

The details of each format are on the companion formats.

In Paged: a fragment would need a host document to be placed into, and a story file would need the frames it was separated from, so reading these files is more than a new parser. Paged reads none of them today. Planned

Frequently asked questions

When would I use an InDesign snippet instead of an IDML export? When you want to reuse a piece of a layout, not move a whole document. A snippet carries a selection of page items and the styles and colours they use, so it can be placed into another document with its formatting intact.

Why do editorial teams use .icml and .icma files? So that writing and layout can happen at the same time. The layout stays in the InDesign document; each story's text goes to an editor as an .icml file, and an .icma assignment groups stories so several editors can work on one layout without editing the same text.

Which part of a package do companion formats leave out? The design map. It is the part that names the spreads, lists the stories and holds settings that belong to the whole document, so a file without it is material for a document rather than a document.