delta property
The first occurrence, standing for all of them.
Its ChannelDelta.channel, ChannelDelta.subchannel,
ChannelDelta.subject and ChannelDelta.property are what the fold
grouped on and are true of every occurrence. Its base and head are
one example of count — deliberately kept, because a shape with no
value attached to it cannot be judged.
Implementation
final ChannelDelta delta;