I am about to start writing a lot of documentation. As I write I find myself repeating things that I have already written about in other parts of the documentation. I for example want to write a "Getting Started" guide. Here, there should be basic explanations of the main interface features. In another document I want to write about how to collaborate efficiently using our tools. In this document I also need the same basic explanations of our main interfaces in case the reader does not know all of them. I would like to do this by embedding a "basic explanation" object, which should be reused in both documents so when updated, both documents are updated. I know that I could do all of this with links, but that makes the reading experience very confusing since I would like to make the text objects very small so they could be reused heavily.
What online collaborative editing tools can support such editing? My preferred editor is Google Docs, but I am open to anything. Google Docs does not support embedding.