Summoning and ownership

I have a couple of fairly simple questions.

First, is the "Summoned" classification, as used in trigger conditions such as "triggering unit is summoned equal to true", something that's preset within a unit's data (and if so, where is it) or is it a state attached when a unit is summoned through a spell?

Second, for a "unit changes owner" event, if I say "owner of ownership-changed unit" does that mean the new owner? I assumed that it would, since the "previous owner" is specifically handled.

I think that creating a unit with a summon spell will automatically give it a summoned classification. As for the owning player, you're probably right, but a simple test can easily confirm this.