Companion formats

Companion formats are the standalone XML files that share IDML's vocabulary but are not full documents.

In short: Companion formats are a small family of files — InDesign Snippets, libraries, story-only InCopy files, and assignment files — that InDesign and InCopy write for narrower jobs than exporting a whole document. They reuse IDML's element names on the inside, so they look like IDML, but none of them is a ZIP package with a design map at its root. Because Paged opens full documents only, none of these formats is parsed today. This page introduces the family so you can recognize each file when you meet it and understand how it relates to the package you already know.

Most of this reference is about the IDML package: a ZIP archive that opens at a design map and contains a whole document. But the same XML vocabulary shows up outside that package, in a small family of related files that InDesign and InCopy write for narrower jobs — a single page item, a reusable library entry, one story's text, an editorial assignment. They look like IDML on the inside, but none of them is a document you can open.

This chapter is here so you can recognize those files when you meet them and understand how they relate to the package you already know. It is reference material about a format family, not a guide to loading them — because today Paged does not load them at all.

Not yet parsedthe entire companion-format family

What counts as a companion format

Four kinds of file travel alongside IDML, sharing its element names while serving a different purpose:

• InDesign Snippets (.idms) — the elements of a single page, captured for re-use.
• Libraries — collections whose individual items are themselves snippets.
• Story-only / InCopy files (.icml) — the text of one story with no page geometry around it, the unit of an editorial round-trip.
• Assignment files (.icma) — the InCopy bookkeeping that maps stories to editors.

The next page, the companion formats, treats each one as a fact: what it contains, how it is marked, and how it differs from a package. When each applies then sets them in the workflows that produce them.

Why Paged parses full documents only

The single thing all four share is structural: each is a standalone XML file, not a ZIP package. That is exactly the shape Paged's reader cannot enter.

Paged's one entry point opens an archive, requires the IDML-package mimetype, and then locates designmap.xml as the document root. A file with no archive, no mimetype, and no design map fails that gate before any of its IDML-looking content is ever examined. A snippet is not a smaller document; it is a fragment that only becomes meaningful when placed into a document, with the host resolving names and styles around it. Paged is a renderer of finished documents, so the document is the unit it reads.

That boundary is not a judgment about the formats — it is where the parser draws its line today. The honest status for every format in this chapter is therefore the same, and you will see it repeated on each page: not yet parsed. What it would take to change that is the closing topic of when each applies.

Frequently asked questions

What are IDML companion formats? Companion formats are the files that travel alongside IDML and reuse its XML element vocabulary without being a full IDML package: InDesign Snippets (.idms), libraries, story-only / InCopy files (.icml), and assignment files (.icma). Each is a standalone XML file written by InDesign or InCopy for a narrower job — capturing one page's items, holding a reusable collection, carrying a single story's text, or tracking editorial work.

Why does Paged parse full IDML documents but not these companion formats? Paged has a single entry point that opens a ZIP archive, requires the IDML-package mimetype, and locates designmap.xml as the document root. Every companion format is a standalone XML file with no archive, no mimetype, and no design map, so it fails that gate before any of its content is examined. Paged is a renderer of finished documents, so the whole document is the unit it reads.

Is a snippet just a smaller IDML document? No. A snippet is a fragment, not a smaller document — it only becomes meaningful when placed into a host document, which resolves its names and styles against what already exists there. It carries no design map to name a root or enumerate stories, so a renderer cannot resolve it in isolation.