The documents listed in HTX catalogue files need not necessarily exist on the local file system. HTX will check to see if they do, and will generate hyper-links to them if they appear to be readable. For files that are not accessible, however, it will generate a reference to the remote document server. This reference will take the standard form using the document name -- not the file name used in the the catalogue file.
Catalogue files can therefore be used as a searchable catalogue of documents that are available remotely. In fact, a document library containing only a catalogue file could be searched by the findme command and any matches would then refer to the remote version of the document, in whatever form it happens to be stored.