The SRD sadly is not a valid source for determining what Spellcasting is nor what Special Attack: Spells is. I maintain that ability to make an action to cast a spell is not a Special Ability. Hence it has no type.
Okay, first of all the SRD is indeed a valid source. It's not a primary source, so if it were contradicted elsewhere you'd have something, but it's not. You know you're in trouble when you start straight up ignoring source material.
Second, Spells is listed as a special attack in the primary source for special abilities (namely the Monster Manual) as well as a host of other books. Special Attacks themselves are listed as being a subset of Special Abilities in the Monster Manual as well, in addition to Fiend Folio. So, that destroys your argument completely.
I keep having to pull out the rules quotes for it, but here you go again... I'll assume from your reference to "Special Attack: Spells" that you accept that there are hundreds of rules quotes that spells are a special attack. In which case, I'll just quote the following:
Special Abilities: Many creatures have unusual abilities, which can include special attack forms, resistance of vulnerability to certain types of damage, and enhanced senses, among others. A monster entry breaks these abilities into Special Attacks and Special Qualities. The latter category includes defenses, vulnerabilities, and any other special abilities that are not modes of attack...
...A special ability is either extraordinary (Ex), spell-like (sp), or supernatural (Su)
Special Attacks and Special Qualities: Many creatures have unusual abilities, which can include special attack forms, resistance or vulnerability to certain types of damage, and enhanced senses, among others. A monster entry breaks these abilities into special attacks and special qualities. The latter category includes defenses, vulnerabilities, and other special abilities that are not modes of attack. A special ability is either extraordinary (Ex), spell-like (Sp), or supernatural (Su). See the Glossary for definitions of special abilities.
Note how very similar these two sections are, and the names of the sections... "Special Abilities" in one case, "Special Attacks and Special Qualities" in the other.
Okay, given those quotes, do you accept that Special Attacks is a subset of Special Abilities, and that any Special Attack must be a Special Ability? Because I think those two quotes (especially right together) are extremely clear.
Moving on...
PHB, DMG and MM1 + erratas are imho the best sources for this issue. For Class Feature: Spells the PHB is the primary source. For Special Attack: Spells the PHB is the primary source (for a small portion the MM1 is the primary source).
Note that the Monster Manual is the primary source for ability types, so since the question now is about ability types, the Monster Manual trumps. Not that that matters, since the PHB doesn't assign a type to spells and thus there is no conflict. But for what it's worth, the PHB does state that all abilities must have a type (when it says that any ability not otherwise given a type is natural... note, any ability, not any special ability. There's a difference, and this is clarified by the Rules of the Game article on the topic).
I suppose you mean Class Feature: Spells instead of Class Feature: Spellcasting as there is no such thing.
Yes, I wrote that for clarity because the same names issue is annoying.
SRD cannot be use as an evidence as it is not a valid source.
False. It is a valid source. It's just not a primary source.
I checked the Celestial Charger and yes it says that it has Cleric levels and that it has Special Attack: Spells. Is Special Attack: Spells a Special Ability? No it is not. I see the contrary.
See above. Special Attack is a subset of Special Ability, so yes, the Celestial Charger does indeed say spells are a Special Ability.
Few rules quotes ahead:
First sentence says unusual abilities. Now, all those abilities are not necessarily Special Abilities as it is not explicitly stated so.
Look at the name of the section. It says quite clearly that all unusual abilities are broken down into two categories, Special Attacks and Special Abilities. And what are those unusual abilities? Special Abilities. If this is unclear for you, hopefully the Fiend Folio entry will clear it up for you, as it's basically the same thing but titled "Special Abilities."
Then these (unusual) abilities are divided between Special Attacks and Special Qualities.
Then Special Qualities is broken down to defenses, vulnerabilities and other special abilities (not modes of attacks). So Special Quality: [Defense] and Special Quality: [Vulnerability] are not necessarily Special Abilities.
No. Just no. Hopefully Fiend Folio clarifies this better for you. It's titled "Special Abilities" so you can realize that's what it's breaking down.
Then we have the glossary in the MM1. It separates Special Abilities and Spells from each other as they have their own subchapters. That alone implies that Spells is something different than Special Abilities.
It's a glossary. It also lists Spell Immunity (Ex) separately from Special Abilities. Do you think that means Spell Immunity (Ex) isn't a Special Ability? Despite the fact that it has that nice little (Ex) tag and fits the definition perfectly? In fact, every common Special Ability in existence is listed in that Glossary separately from the main "Special Abilities" entry.
Special Attack: Spells cannot be extraordinary because they are magical, become suppressed or fail in antimagic field, and can be disrupted (e.g. casting a spell in combat).
Once more, with feeling: You CAN still cast spells in an antimagic field, so the ability is not suppressed. But the spell itself is. This is different from Spell Like Abilities... you can't even try to use them in an antimagic field, because you lose the ability. Again, ability != action.
Nor it can be spell-like or supernatural. I'll leave out rules quotes as I assume this is not disputed. In fact Special Attack: Spells is not a Special Ability.
Can I assume this part is considered answered by the combination of the MM and Fiend Folio quotes that directly state that Special Attacks are Special Abilities? If you need, I've got a Rules of the Game quote to help too...
Here it says that "can cast" i.e. the generic ability to make an action to cast a spell. Which is what I maintain that Spellcasting (generic ability) is just an action to cast a spell. And that action is not a Special Ability.
There is no such thing as a Generic Ability. You just made that up. It doesn't exist. Seriously, find one rules quote that says "Generic Ability." I can bring up quite a few that state that all abilities must have a type, if you need, but you've probably seen them before. Rules of the Game: AAP, PHB 180, so on and so forth.
Is making a standard action (to cast a spell) a Special Ability? No it is not.
The ability to do so is, as defined in like 10 different sources.
If it were it could not be ex as it can be disrupted, nor it can be sp, su or na for other reasons. Hence it is not a Special Ability.
Action disrupted, ability not. You can never be made to lose your
ability to cast spells. But the spells themselves can be disrupted.
Also note that Special Attack: Spells use the same rules as the characters with few stated exceptions. So it means that the primary source for Special Attack: Spells is in fact PHB.
The PHB doesn't contradict. Primary source rules do not apply here... but if they did the Monster Manual is the primary source on Special Ability types (which all Special Attacks explicitly are).
So let's do an exercise and take our finely seasoned delicious king-fish the Aboleth Mage (MM1 p.8-9) to the table.
It has the following SQ and SA fields:
Special Attacks: Enslave, psionics, slime, spells
Special Qualities: Aquatic subtype, darkvision 60 ft., mucus cloud, summon familiar
How do we categorize these unusual abilities?
They're all Special Abilities because as the rules say over and over all Special Attacks and Special Qualities are.
Enslave: It's Su because it says so in the entry.
Psionics: Sp because it says so in the entry.
Slime: Ex because it says so in the entry.
Spells: Ex because it's a Special Attack, which by MM 6 and FF 8 and Rules of the Game means its a Special Ability (and which is a Special Ability by SRD as well), which by MM6 and the MM Glossary and FF8 and SRD means it's Ex, Sp, or Su, which by the reading of the Antimagic Feat and PHB 180 and a bunch of feats in FC1 can't be Sp or Su, meaning it's Ex, QED.
Aquatic Subtype: Na. Its inherent to the physical nature, and breathing and normal physical movement modes are always Na. Note that most subtypes are a mix of Na, Ex, Sp, and Su abilities, which is why subtypes are always listed under special qualities even though a few of them (Aquatic, Animal, a few others) are completely Na.
Darkvision 60ft: Ex. Na abilities are generally ones that could exist in real life, whereas stuff that couldn't is always Ex. Plus, Na abilities only cover the five basic senses (as per RotG) so special senses are always Ex (if they're not magical).
Mucus Cloud: Ex because it says so in the entry.
Summon Familiar: Not sure at all. From the description it could be Ex (you lure the critter in with 100 gp of snacks?), Sp (you summon it with something spell-ish), or Su (you summon it with something not so spell-ish). I'm inclined to say Sp.
Ok, I'll try.
Special Attacks:
Enslave (Ex) - that's easy as the description has the type. Special Ability indeed.
psionics (Ex) - easy, same as above
Okay seriously are you just trolling me? The entry clearly says these are Su and Sp, respectively. The description decidedly does not say Ex.
slime (Ex) - easy, same as above
Easy because it says so.
spells - ouch much harder; I maintain that this is only about performing actions thus do not need a type at all. MM1 provides for a generic term unusual ability.
Funny how everything else in the category has a Special Ability type. Seems like one might see a pattern to these here Special Attacks. Almost like they're all Special Abilities. And since "Unusual Ability" is always used as being synonymous with "Special Ability" your claim here is pretty funny. Notice how it says it's talking about Unusual Abilities in the quote from MM 6 your provided... and then goes on to mention that the definition of Special Abilities is in the glossary. Seriously, they're synonyms.
Special Qualities:
Aquatic subtype - um, not a Special Ability at all; Defensive unusual ability?
You're right that this doesn't seem like a Special Ability, but remember that the majority of subtypes are (because they have Ex, Sp, and Su abilities mixed in, like racial Darkvision and Aura of Menace for Angels). Much like how Spells are always listed as a Special Attack even though a creature might have no offensive spells at all, and thus it would be a better fit in Special Qualities, subtypes are always listed in Special Qualities even though a few of them don't actually have any Special Qualities in them.
darkvision 60 ft. - um, same as above
It's Ex. Only basic real life senses are Na. Other (non magical) senses are always Ex. See the Rules of the Game if you need a reference.
mucus cloud (Ex) - easy as the description has the type. Special Ability indeed.
Yes.
summon familiar - huh, 24 hour action that uses 100 gp of magical materials (PHB p.54), not a Special Ability at all and definitely not Ex as this action could easily be disrupted. Defensive unusual ability?
You can't say something's "not a Special Ability" and that it's an "unusual ability" at the same time. They're synonyms.
As you can see the categorization based solely on Special Abilities is simply not possible nor a valid way to do it. The Class Feature: Summon Familiar is yet another example where categorization with Special Ability tags does not work.
All I can see is that you're completely failing to read the rules, especially since you just labeled two abilities as Ex and claimed they said as much even though they're listed as Sp and Su.
So Special Attack: Spells is not a Special Ability. It is a Class Feature that only enables specific action (to cast a spell).
Yeah... I really hope that FF quote clears this up for you. You've just spent a whole post misunderstanding the MM 6 post and being completely contradicted by the FF 8 post (which backs up and clarifies MM6). And to be clear, if an ability is not a Special Ability, it's Natural:
Natural Ability: This term is a catch-all for just about anything a creature can do (or characteristic that it has) that is not extraordinary, spell-like, or supernatural. Natural abilities include most speed ratings (some very high speeds are not "natural," see the section on the alter self spell), mode of breathing (lungs, gills), natural armor and weaponry, general appearance, body type, and the presence or absence of the five basic senses (sight, hearing, touch, taste, pain). When polymorphing, you generally lose your own natural abilities and gain those of your assumed form.
JaronK