ACI BD concept - vlan interface with secondaries?

[tsmarcyes]

In ACI discussions, its always mentioned that BDs are NOT VLANS.   The most common argument are that vlans equated to one subnet and thus since you can have multiple subnets in a bridge domain, they are therefore not the same as vlans.  However, in traditional networking (although typically not recommended), we could have multiple subnets on a vlan (vlan interface) using the secondary command after the ip address.  Thus, you can have multiple subnets per vlan even in traditional networking.  And guess what, all those subnets are subject to the same flood domain since they are all in the same vlan.  Many try to equate BD to PVLANS, but to me the vlan interface with secondary ip addresses seems closer as private vlans are typically used to segregate traffic within the vlan while if Im not mistaken the default behavior in ACI for BD is to allow communication between all subnets, just like a vlan interface with secondaries.  Although there are still other constructs involving EPGs, contracts, etc, that then take the BD beyond this simply concept, if we are simply talking about the BD itself, would it not be logically correct to compare it to a vlan interface that MAY have multiple subnets (secondary ip addresses).