title: Text file type that supports in-line notes
body: <p>The idea is simple: A text file that supports attaching additional text as notes (or tags or comments) to parts (sentences or words) in the main text body. I would like to apply such a file type specifically in a simple application for viewing research work, so that citation can be attached in-line to sentences or phrases within a work. I mean, has anybody come across such? Has that wheel been invented already? even if in a rudimentary fashion or as part of a larger non-proprietary file type.</p>