Repositories can increase their value by supporting commentary, annotation and peer review activities. The functionality to allow these activities does not necessarily need to be provided by the repositories themselves but can rather be provided by third party services or tools that specialize in the creation of overlay content. By supporting the creation of overlay content in this manner, repositories can begin to reposition themselves to the centre of scholarly communication and promote discussion and collaborative work. Achieving a level of interoperability between repositories and such third party services is essential, especially with regard to the manner in which overlay content is expressed, and the way in which the repository is made aware that overlay content was created. This allows the repository to surface the overlay content by linking to it, by ingesting it, and by exposing it to aggregators. In order to be able to unambiguously connect overlay content with its creator, global identification and authentication of users that generate it is essential [see behaviour Identification of Users and behaviour Authentication of Users].
With regard to technologies aimed at informing a repository that overlay content was created, and the manner in which a repository can expose this information, see [behaviour Collecting and Exposing Activity Metadata].