+/// The number of blocks such that if:
+/// `incoming_htlc.cltv_expiry < outgoing_htlc.cltv_expiry + cltv_expiry_delta`
+/// then we need to fail the HTLC backwards. When forwarding an HTLC, cltv_expiry_delta determines
+/// the outgoing HTLC's minimum cltv_expiry value -- so, if an incoming HTLC comes in with a
+/// cltv_expiry of 100000, and the node we're forwarding to has a cltv_expiry_delta value of 10,
+/// then we'll check that the outgoing HTLC's cltv_expiry value is at least 100010 before
+/// forwarding. Note that the HTLC sender is the one who originally sets this value when
+/// constructing the route.