39.4 Declaring File Type Support
A key step in implementing document support is declaring the file types which the app supports. The DocumentGroup user interface uses this information to ensure that only files of supported types are selectable when browsing. A user browsing documents in an app which only supports image files, for example, would see documents of other types (such as plain text) grayed out and unselectable within the document list. This can be separated into the following components:
39.4.1 Document Content Type Identifier
Defining the types of file supported by an app begins by declaring a document content type identifier. This is declared using Uniform Type Identifier (UTI) syntax which typically takes the form of a reverse domain name combined with a common type identifier. A document identifier for an app which supports plain text files, for example, might be declared as follows:
The document content...