1. A tangible computer-readable storage medium having computer-executable instructions for managing data associated with computer-generated documents, comprising: storing structured data items that are associated with a document in a data store that is maintained separately from document data for the document; wherein the document data defines a primary presentation for displaying the document; wherein the structured data items are represented by Extensible Markup Language (XML); wherein the structured data items are metadata for the document; wherein the structured data items remain associated with the document until the structured data items are removed from the data store; and formatting the structured data such that an application programming interface (API) is exposed to a plurality of different client data consuming applications for allowing programmatic access to the structured data items by each of the data consuming applications; wherein execution of the API provides the ability to access the structured data items within the data store while the document is open for editing and when the document is closed for editing; wherein the API that allows the programmatic access to the structured data items by the data consuming applications comprises allowing the plurality of data consuming applications to access a same structured data item at the same time; wherein the API allows any of the data consuming applications to store structured data items within the data store; and registering for notification of changes by the data consuming applications; determining when a change is made to one of the structured data items using the API; and when a change is made, notifying the registered data consuming applications of the change; in response to the notification of the change, queuing a side-effect change by one of the data consuming applications, wherein the side-effect change is generated based on data related to the notified change; and notifying the registered data consuming applications of the side-effect change.