Writers of core rules books in general understand that they are creating a foundation for an entire gaming community. They put a lot of effort into making sure their rules are unambiguous, that they play well with other rules, that there are as few potential misinterpretations as possible. Usually many eyes look at these products. There are rounds of playtesting, fact-checking, and proofing.
Not so, it seems clear to me, for Splat Books, including the Pathfinder Advanced Players Guide (APG). Too often, too few eyes read this stuff over. Too few gamers try the rules out. And it shows. Here are a couple examples from the APG, starting with a Stone Oracle ability.
Clobbering Strike (Ex): Whenever you score a critical hit against an opponent with a spell that requires an attack roll, you may immediately attempt to trip your opponent as a swift action. You do not provoke an attack of opportunity as normal for this trip attempt. You cannot be tripped in return when using this ability.
Huh? When you crit with a spell that requires an attack roll, you can trip your foe too? Even with ranged spells? Hit a foe with an Acid Arrow or Ray of Enfeeblement, and you can trip them? Using your Str stat as usual? This is just weird. I can't even begin to think what they were intending. Only melee touch attack spells? What about touch spells delivered by a familiar? Very poorly written rules.
Consider the fourth level Battle Herald, who gains the Bardic Performance Inspire Greatness ability, and advances the number of people affected as the battle herald gains levels. BUT it fails to note if it uses only daily rounds of Bardic Performance or if the character can also draw on Inspiring Command rounds per day. Ugh.
And under the Voice of Authority ability, the battle herald gets to grant bonuses to allies: "In addition, her allies gain a bonus equal to the battle herald's class level on Perception or Sense Motive checks to hear her commands or interpret her secret messages conveyed with Bluff." HOWEVER, per the PF Bluff skill, "the target automatically understands you." There is NO check to "interpret her secret messages." So this PrC gives a bonus to something that does not exist in the game. This is just so sloppy! What very very poor game design. I mean, really! The creator of these published rules in an important secondary text just does not even know the basics on how skills work.
Also, take a look at the Weapon Cord ... first off, ugh! Look at this: "Unlike a locked gauntlet, you can still use a hand with a weapon cord, though a dangling weapon may interfere with finer actions."
What kind of vague and ambiguous rule is this? MAY interfere with finer actions? What does that even mean? First off, what is a "finer action"? AFAIK, it is an undefined and meaningless phrase. Can you cast a spell? Use a wand? Pick a lock? No guidance at all! And what does "may" mean? There's a chance of success? 50%? 1%? 99%? Make a dex check? Impose your armor check penalty? It's all just one huge splat sound coming from a poorly written splat book!
And what does "switch weapons" mean? That's another undefined phrase. Is there a "switch to a different weapon" action in the game? Does that mean "draw a weapon"? "move a weapon over from another hand"?
If I were forced to adjudicate these questions as a DM, I would houserule that (a) you cannot cast a spell with a hand from which a weapon is dangling, and (b) you cannot make any attacks at all with a hand from which a weapon is dangling, whether with another weapon, a touch spell, claws, an unarmed attack, whatever. Also no two handed weapons or bows. You can hold a shield, use a wand or other magic item (but not to make an attack roll), hold a torch, etc.
To players who complain that my opinion seems restrictive, I would say, "Look, you're getting immunity to disarm for one silver piece. Be happy!"
For more on the APG and splat books generally, read my all splat books are bad screed.
This screed was posted here on 23 Aug 2013, but it was mostly written as a message board post on 21 May 2011.