There are a few bits about damage reduction that I'm unclear on in pathfinder, specifically...
Easy one first; Do cold iron/silver weapons equivalent (+3) count as magic for purposes of ignoring DR? This is certainly implied, but not categorically stated as I read it.
Is the only way to get an alignment based attack in a weapon to cast either align weapon, use a +5 weapon or be a monster with a 10/lawful (for example) reduction and use a natural attack? Or is a alignment monster using it's natural attacks counted as damage of that type , e.g. an Morlock is CE, do it's attacks count as Chaotic?
If you are a monster with alignment based reduction (eg 5/Lawful) do your natural attacks have no effect on any other alignment DR other than lawful? I.e. if a summoners Eidolon has 5/Neutral are a monster with DR 5/Lawful attacks still reduced by 5?
If a monster has two types of DR what do it's attacks natural attacks count as, eg a Kyton has DR 5/silver or good, do it's attacks count as silver (+3) or alignment (+5)?
Speaking of Eidolons; the evolution "Damage Reduction" (p63 advanced players guide) gives the Eidolon DR5/alignment; does this now mean that the Eiodolons natural attacks will now count as ignoring DR for that alignment (and cold iron, silver, adamantantine, maybe magic) as alignment based attacks are equivalent to +5. Note that Eiodolons also have a cheaper evolution "magic attacks" (p60 APG) as well.
If a monster has DR of (Greater Earth Elemental for example) 10/- what do it's attacks count as? A monster with 10/magic has attacks that are counted as magic, if I read it correctly, but I don't see text for monsters with the '-' reduction.
Certain massive monsters (Rolling out the Tyrannosaurus again) have no DR at all, but are massive beasties; do their attacks not count in any way against DR? (Not that the T-Rex needs to worry much about DR, it does massive amounts of damage!)
Spells aren't affected by DR at all? So your common or garden magic missile happily does full damage against a monster with 20/- reduction?