One caveat for external links to the TEI Guidelines: since the web version at http://www.tei-c.org/Guidelines/P5/ is unstable and will be updated at each new release, you must point to the archived versions in the ‘Vault’ section of the TEI website. There, you can find an archive of all previous TEI releases and their documentation. Follow the links to the exact version you're referencing in your article (even if it's the current version), and use them for your external hyperlinks. In the examples above, the first link points to the documentation of version 2.2.0 of the TEI Guidelines, while the second link points to version 2.5.0.