An editor is responsible for editing the specification for one module. Each module must have one and only one editor. He/she is responsible for editing the specification, leading the discussions, trying to find a consensus when appropriate, etc. Here are several infos for editors.
The specifications are written using W3C's XMLSpec format. Actually there are a few modifications to that format, defined in a separate RNC schema importing the original one. Same for the stylesheet to get the XHTML result. You can find all needed material in the repository.
Look at Specification for more information.