Each schema locating file specifies a list of rules. The rules from each file are appended in order. To locate a schema each rule is applied in turn until a rule matches. The first matching rule is then used to determine the schema.
Schema locating files are designed to be useful for other applications that need to locate a schema for a document. In fact, there is nothing specific to locating schemas in the design; it could equally well be used for locating a stylesheet.