You are right that in the BOLT3 Scripts the revocation path pays only to a single public key, the revocationpubkey.
In order to keep the same restriction with a single pubkey, the revocationpubkey is derived based on both a secret generated by the local node and one by the remote node.
Without the part of the secret only known to the local node, the remote ...
A bit is a binary digit with the two possible expressions 0 and 1. Binary data is often represented as hexadecimal in writing as that is more compact and human-readable. Hexadecimal (base 16) encodes the (decimal) numbers 0 through 15 with the symbols 0-9 and A-F (where A-F represent 10-15).
A few examples (subscript indicates base):
110 = 116 = 00012
510 = ...
It was added as a compromise against more complicated ideas, actually. Base plus percentage is a pretty standard fee structure, so I went with it.
If I'd been more familiar with the finance world, it would have been expressed in basis points, though, not ppm.