I have noticed that quite a lot of Wikibooks use links to Wikipedia regularly. At the same time however, they link to other Wikibooks and other chapters of the same book. It is, of course, impossible to tell wether the link is internal, to another book, or to Wikipedia without clicking on it or hovering over it. This can be extremely bothersome to a reader, who may want to read a Wikibook or chapter on the subject, but not a Wikipedia article. The reader can not tell until he or she has clicked on it where it is going. An example from C++ Programming:
Bjarne Stroustrup, a Computer Scientist from Bell Labs, was the designer and original implementer of C++ (originally named "C with Classes") during the 1980s as an enhancement to the C programming language. Enhancements started with the addition object-oriented concepts like classes, followed by, among many features, virtual functions, operator overloading, multiple inheritance, templates, and exception handling. These and other features are covered in detail along this book.
The first two links link to Wikipedia pages, the second links to a Wikibooks subject page, and the rest link to other chapters of the same book. Wikipedia links are useful, of course, because they can link to related pages that the Wikibook does not deal with. For example, a Wikibook about the French language may say that French is also spoken in Monaco, but a reader might like to know where Monaco is and the book does not want to waste time explaining it, as it is not directly relevant. A link to Wikipedia becomes very useful in cases like this. But Wikibooks should try not to rely on Wikipedia too much, and so a link to it should appear different than one to a chapter within the Wikibook or another Wikibook. After all, books should be encased within themselves and not need to rely on the explanation of an encyclopedia or another book. Can you imagine how annoying it would be to have a math text book that makes you go look up what a quadratic function is?
So my proposal here is to use the project-wide CSS page to make all links to other projects look different than inter-chapter and inter-book links. This could be done with a slightly different color or font, or something similar to (but different than) the way external links appear (with the arrow thing like this - external link).
This would really facilitate the reading experience, and make this project less dependent on Wikipedia. After all, Wikibooks is not an encylopedia, and so does not have to conform to the formatting standards of Wikipedia.