Are there online services for compiling documentation with the possibility of interspersing parts of other documents?

Question

Documentation

Situation:
When writing documentation (for example, describing web pages), in the case when descriptions of different parts of one system are transferred to different developers, a situation occurs in which it is required to describe all the standard elements in the document, which, in theory, can be taken out in a separate document.
Most often these are different documents, which leads to the fact that the developer must "jump" through several documents, relying on links in the document.
Task:
When writing a document, it is required to add text from documents of information donors in such a way that:

• Parts (despite the fact that all paragraphs in the documents are automatically numbered) from other documents were easily interspersed in the text, with a link to the document from which the text was taken.
  
• Changes in the donor document were immediately displayed in the place of inclusion.
  
• When deleting a donor document, the interspersed text remains with the appropriate sign.
  

Does anyone have any decisions to make?

Answer 1

You need (at the same time):
1. single sourcing technical documentation - Docbook or DITA.
2. inclusion of parts - xinclude.
3. processing at the xslt level.