Currently, you can add instructor notes. From such notes, you are welcome to link to your own material, perhaps a google doc, or web page, or slides.
Eventually we do hope to support having instructors create and add their own material directly in a zyBook. But there are several tricky issues.
One issue is maintaining consistency of terminology, quality, and style, which is surprisingly hard; abrupt switches within a zyBook may not be a great student experience. We are working towards creating guidelines, processes, and some automation to help instructors make material that could fit into a zyBook.
Another issue is maintenance. If instructors create their own material that extends or modifies our material, then it becomes harder for us to maintain our material. For example, if we teach X, and an instructor adds material on Y, and we later update our material to teach X and Y, then students may get confused with two presentations of Y, and the instructor may get annoyed that he/she spent effort that is now “wasted”. Or, if an instructor creates a section between sections A and B, and later we merge A and B, where should the instructor’s section go? Or, if we decide to replace term U by term V throughout our material, instructors may be frustrated since their material used term U. Dozens of such maintenance details exist.
There are also issues related to how such material would be tracked by instructors, how an instructor would include previously created material into new class zyBooks, whether instructor material is maintained as one source or whether material is cloned each term, how such material would be shared with other instructors at the same school (which also introduces copyright issues), etc.
Many of the issues are due to modern learning material being much more dynamic than traditional static textbooks. It’s a new frontier, and while we’re learning as we go, we wish to share that ideas are often harder to implement than they may seem.