document difference between EDF and EDF+

[robertoostenveld]

annotation channel, anything else?

[sappelhoff]

Related:

• Is this reader also for EDF+?
• Is EDF+ supported by BEP_006, or are we really just supporting EDF? EDF+ is definitely supported

This also relates to @chrisfilo 's recent remark:

There was previously some talk to do rudimentary validation of EDF headers in the validator (for example using https://github.com/Pixpipe/edfdecoder) - where does this stand?

... because the referenced edfdecoder works only for EDF, and not EDF+

[palday]

At the moment, I think it's just EDF. I might be willing to consider adding EDF+/GDF/BDF support in the distant future, but I'm not even sure if it makes sense to have it all in the same package or whether there should be a constellation of packages (possibly with a convenience package that imports and wraps them all, a bit like tidyverse in the R world).