The inherent fragility of hypertext links is a problem faced by any project that needs to maintain a collection of related documents in hypertext form. The documentation for software projects typifies this. However, software documentation also suffers from an additional problem because it is usually distributed and installed along with the particular items of software it describes. This means that any sub-set of the complete documentation set must also be viable in its own right.
To give an example, a particular site may only have installed one or two items out of a complete collection of software, and so may only have a couple of documents that relate to the installed software available locally. This means that many of the cross-references that these documents make will be to other documents that do not exist on the local system. Ideally, these links should not simply fail.
The problem can be solved by using a document server to provide access to the missing documents from a central archive, where a copy of all the documents is maintained. A reader with any of the documents installed locally will then potentially have easy access to the entire documentation set, albeit with some time penalty when accessing non-local documents. One of the functions that HTX performs, therefore, is to generate appropriate requests for remote documents for processing by a central document server.