Create a project collection
Apple documents File > New Collection, then dragging fonts into it, or selecting fonts and using New Collection From Selection. Rename the collection in the sidebar. Adding a font to a collection leaves it available in its previous location; the group is an organizational view.
Distinguish collections and libraries
Apple says user-created collections appear in the Fonts window used by some apps such as TextEdit, while user-created libraries do not. Choose the grouping for the workflow you need rather than assuming every sidebar item becomes an identical menu in every application.
Review a problematic resource
Apple’s validation guide documents File > Validate Selection or Validate File, with details under each entry. It also describes File > Resolve Duplicates and a manual review option. Preserve source information so two releases with similar names can be understood before deciding which copy to retain.
Keep the working set clear
Organize a collection around an actual project or text role. Keep the family, style and supplier with your notes, especially when another editor must reproduce the design. The separate Mac installation guide explains how a new resource reaches Font Book in the first place.
Your questions, answered.
Does adding a font to a collection move it away from every other collection?
No. Apple states that it remains available in the previous location.
Do Font Book libraries appear in every app’s Fonts window?
Apple distinguishes libraries from collections and says created libraries are not shown in that window.
Sources & background
Sources supporting this page’s explanations. Practical examples are our editorial suggestions.