Complete Divine on Extra Domains says that when a creature that casts arcane spells gains a domain then
If she is a spellcaster who keeps a spellbook as a wizard does, then she must find or purchase a scroll of that spell and pay the usual price to scribe the spell into her spellbook. In cases where the spell is only divine the wizard may scribe a divine scroll into his book. The wizard then may memorize one domain spell of each level each day. (20)
(Readers, try not to fixate on the pre-Third Edition term memorize; assume Complete Divine means prepare.) While Complete Divine provides examples of how an extra domain affects the casting ability of, respectively, a paladin, a cleric, then a sorcerer, it doesn't provide an example of how an extra domain affects the casting of a wizard.
Is this one domain spell of each level each day in addition to the wizard's normal spell allotment—therefore, essentially, an extra spell slot per day at each spell level above 0 but that's only capable of holding a domain spell—, or does that phrase limit the wizard's spell preparation options but leaves unchanged the wizard's spell slots? Or is there another altogether different way to read this that I'm overlooking?
An example: Travaran is a human diviner 7/divine oracle 6. A level 1 class feature of the prestige class divine oracle (CD 34–6) grants him access to the domain Oracle (Spell Compendium 277–8) that has as its 1st-level domain spell the 1st-level normally-Sor/Wiz spell identify [div] (Player's Handbook 243).
Until he gained that first level of the prestige class divine oracle, Travaran—who already had the spell identify in his spellbook—could prepare and cast as many times as he wanted the identify spell (within the limits of his spell slots and casting ability, of course). After taking that one level of divine oracle and gaining access to the domain Oracle, though, can he now, for example, prepare an additional identify spell at each of his spell levels 1st through 7th? Or can he now, for example, prepare the identify spell only once at each of his spell levels 1st through 7th? Or, y'know, something else?