When looking at, say, Wikipedia pages, it is immediately recognizable whether any given link is internal or external. With Wikidot.Com wikis, this is not the case - you have to hover the mouse pointer above it to see where any given link leads.
Yet the internal software clearly must recognize which link is which - but this doesn't show in the final HTML code of the page. Therefore, I propose giving external links a class of their own (say, "ext-link") so that you can customize CSS files to give such links a different appearance.
Note: I do realize that it is possible to give individual links different appearances by inserting custom classes and using the "div class" tag. But I really don't want to do all this manually…