The ExternalAnnotationSearchRule class is used to specify the annotation type, the prefix pattern, the suffix pattern, and if the original file extension is included in the external annotation file to be searched for by ThumbnailXpress. If a file is found that matches the criterion then it will be used to draw annotations of the thumbnail.
For Example: If the image being thumbnailed is "House.tif", and the prefix pattern is "Annot_" and the suffix pattern is ".external", and the IncludeFileExtension flag is true then it would look for an external annotation file named: "Annot_House.tif.external" If the image being thumbnailed is "Test.jpg", and the prefix pattern is "" and the suffix pattern is ".annot", and the IncludeFileExtension flag is false then it would look for an external annotation file named: "Test.annot"