Described is the annotating of computer document content, particularly editable content, by saving annotations in a separate annotation store, and mapping the annotations back to the content. By mapping, no data are added to the original content at runtime, and only minimal data need be added to the content when persisted. An annotation is anchored to a piece of runtime content, such as upon creation of the annotation, by maintaining annotation data as well as start and end pointers mapped to the annotated piece. Upon saving the content, information (e.g., an anchor marker including an identifier) is persisted with the piece of content to allow the annotation to be re-anchored to the piece upon subsequent reload. For example, when loading content from persistent storage that includes an annotation identifier, the annotation identifier is processed to locate a start and end of the portion and an annotation in the annotation store.