Conditions that affect the availability of, or method(s) of access to, an item. Typically used for real world items such as an [ArchiveComponent](http://schema.org/ArchiveComponent) held by an [ArchiveOrganization](http://schema.org/ArchiveOrganization). This property is not suitable for use as a general Web access control mechanism. It is expressed only in natural language. For example "Available by appointment from the Reading Room" or "Accessible only from logged-in accounts ".