2.2.2.2.3 FileExtension Element
The <FileExtension> element contains the definition of one file type such that the remote resource is capable of opening documents of that type.
Name: The name of the file type, which MUST be preceded by a dot (for example, ".txt"). This attribute value SHOULD be unique among all <FileExtension> elements contained in the <Resources> element (section 2.2.2.1.3).
PrimaryHandler: This attribute is reserved for future use and MUST be set by the server to the xs:boolean value of True.