Channels marked as "bad" have further specification

Hi,

I presented this idea at a previous office hours. I work in a lab that records ieeg data from epilepsy patients. Due to the nature of the data, apart from some channels having a poor signal quality there are some of channels that show interictal activity (sharp spikes that confound just about any analysis), are seizure onset zones, are outside of the brain or surrounded by damaged tissue such as a lesion. My group likes to apply one or more of these tags to channels when they apply as they assist in analyzing and interpreting this data. My initial thought, and that of someone else, was to place this information in an Annotation object like so:

sozChns = ['RDa1','RDa2']
spikeyChns = ['RDa1','RDa2','LDh1']
outChns = ['RDh16','LIp16']
chan_annots = Annotations(
    onset = [0,0,0,0], # Onset and duration indicate that these annotations apply to the entire block and not a section
    duration = [0,0,0,0],
    description = ['soz','interictal','out'],
    ch_names = [ sozChns,spikeyChns,outChns ]
)

We can then aggregate all these channels into the info['bads'] list but it's useful, especially when looking at something like seizure networks, to be able to label channels using these other tags. I've also considered adding this information to _raw_extras dictionary in the Raw object but it wouldn't survive an io round trip. It can be saved in a separative text file (maybe that's how it's done using BIDS) but it's more convenient if it can be saved within the object.

To summarize this long post, it would be nice to be able to apply tags of some kind to channels.

Start by reading the Annotation and Raw representations, including info['bads'] and _raw_extras, and review how BIDS or other I/O paths handle channel metadata. Define the supported channel tags and their persistence requirements, then add coverage showing that tags remain available after an I/O round trip without replacing the existing bad-channel handling.