This is a timely discussion. I have been thinking about how to deal with prefixes defined by the #+link: keyword which is directly related to this question.
I think the following might be a solution that also avoids the issue brought up by Arne. The original "bug" cannot be resolved because bare URIs have syntax that conflicts with Org syntax. However I think we can do better than directing users to org-link-set-parameters. My suggestion is as follows. Schemes/prefixes defined by the #+link: keyword can be used without surrounding syntax markers but may not contain spaces etc. To support this Org parsers should always parse prefix:suffix as a _putative_ link which must then be checked against a list of known schemes that are either built in or have been declared by the user to indeed be legitimate schemes. In the tel: case, the way to solve the original bug is simply to add the line #+link: tel tel: which would tell Org that e.g. tel:555-555-5555 is a real uri, and that it should expand to itself. At the same time this solution would avoid Arne's issue (which I also have in some of my documents where I have use fig: and tbl: as prefixes in names and reference them via [[fig:figure-name]]) because the parser would only treat prefix: in an internal link as a scheme if it is defined explicitly by the user in a #+link: keyword or in their init.el. Thoughts? Tom
