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I've noticed normal channel IDs have "UC" at the start while automatically generated ones have "HC". Normal playlists have "PL" but special ones, like uploaded or favourite videos, have "UU" and "FL", which however doesn't apply to autogenerated channels, they have "LP". That's what I've found so far. Is there any list of all these prefixes with their meaning?
Edit: Playlists based on a specific video begin with "RD"+the video ID.
There is not a guideline and they may always change. I strongly suggest not to depend on them but the pure API methods.