instance property
public string Extension
The extension(s) of this file type. Separate multiple extensions with a pipe (|).
Here's how the JPEG preset is defined with two possible extensions:
public static readonly SupportedFileType JPEG = new SupportedFileType {
Name = "JPEG Image",
Extension = "jpg|jpeg",
Owner = false,
AppleUTI = "public.jpeg",
MimeType = "image/jpeg"
};