dhcpcd-discuss

I have installed the new `raspberrypi-net-mods` using `dhcpcd`. This works, but I am trying to understand why and how.
I have read the `dhcpcd` and `interfaces` `man` pages but these do not seem to apply to the actual interface.
I have asked questions on a few RaspberryPi and Linux forums and not received any sensible comments, although there see to be others who are confused.

The `/etc/network/interfaces` used to contain `iface eth0 inet dhcp` which has been replaced by `iface eth0 inet manual`
Boot messages with dhcp show 
	[FAIL] Not running dhcpcd client because /etc/network/interfaces defines some services that use a DHCP client.
I presume this is from `resolvconf` or similar.

Where does the IP address come from? This seems to allocate the same IP reservation from my router.

Is `/etc/network/interfaces` involved in the `dhcpcd` process?

Using the supplied `raspberrypi-net-mods` configuration both my Ethernet and WiFi seem to be active (although the router seems to think they have the same MAC). Previously using `wpa-roam` in `/etc/network/interfaces` only activated WiFi if Ethernet was not connected, but this no longer seems to work.

I am trying to work out a configuration which will let my Pi work normally with my home network, but allocate a `static` address so I can connect to the Pi over Ethernet (or ad-hoc WiFi) to my Mac in a remote environment with no router or internet access.