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.
HTX Hypertext Cross-Reference Utilities