Christian said:
There's a specific order for leveling events, listed on pg. 58 of the PH 3.5. It goes:
1. Choose Class
2. BAB
3. Base Saves
4. Ability Score
5. Hit Points
6. Skill Points
7. Feats
8. Spells
9. Class Features
Which can make it sometimes difficult to get into PrCs or qualify for certains feats. Example:
Say you are a Scout3/Ranger 6. At 6th level, you have all the prereqs you need to get the Greater Manyshot feat (located in the XPH) except one. You are lacking the Manyshot feat. A Ranger gets this feat at 6th level, but since it is a class feature, he doesn't get it until the end of the operations, and by that time, he would have had to picked his feat already.
A character can gain a feat at the same level at which he or she gains the prerequisite.
This could be read to mean, if you gain the prerequisite then you are eligible for the feat. The problem is, you still have yet to gain the prereq, which hasn't happened yet.
Let's say we are a Rogue 1 and just his 2nd level and take a level of Fighter (Rogue 1/Fighter 1). Our BAB is now +1, so if we want to use our Bonus Feat (a class feature, last step) to pick up Weapon Finesse, we can, because by that time, we've got our prereq met (A character can gain a feat at the same level at which he or she gains the prerequisite).
However, since our Scout3/Ranger 6 does not met the prereq by the time we reach Step 7, he can't get it (he'll meet the prereq at Step 9)
Unless you assume there is no "order of operations", in which case the list is simply a check list of things to do. Then that sentence (A character can gain a feat at the same level at which he or she gains the prerequisite.) makes sense and we can pick our class feature before taking our feat.
Just one way to interpret this...
Edit... fooled by hong's misrepresentation of the prereqs for Weapon Focus, so changed it to Weapon Finesse.