Watercolor—especially an expanded watermedia version of watercolor—is an exciting and expressive medium. You can do almost anything with it, particularly when using the many water-based products, papers and canvases that are available to us.
Watercolor has been maligned as an extremely unforgiving medium. While this is true to some extent, even purely transparent watercolor is more easily manipulated than you might imagine. As you go through the step-by-step demos, you will see where paint has been gently lifted or not so gently scrubbed, then repainted in such a way as to revive freshness. Then, in a worst case scenario, painted over with gouache, casein or acrylic.
Regarding opaque media, lest you think the addition of an opaque medium such as gouache is merely a last resort fix, it must be said that opaque mediums can add beautiful qualities and dimensions to a painting that you might not be able to achieve otherwise. It must also be acknowledged that opaque media are highly respected in their own right, so why not incorporate any and all media to improve and complete a painting?