For editing the documentation, typically you should not use formal XML editors. Such editors normally autoformat existing documents to fit their own standards and/or do not strictly follow the docbook standard. As examples, we have seen them erase the CDATA tags, change 4 space separation to tabs or 2 spaces, etc.
The style guidelines were written in large part to assist translators in recognizing the lines that have changed using normal diff tools. Autoformatting makes this process more difficult.