Questions About Unit File Stuff

I've been looking through the unit files and ATM their are a few things i'm having trouble understanding sure to the vague descriptions.

Namely the Spear, Light-Spear, Long_Pike and Short_Pike weapons attributes.

What’s the differences exactly?

Spears have 2 entries and Light_Spears have one, but I’m unsure on things to a degree. Namely do Light_Spears really get no penalties against infantry as the description suggests, or are they just weaker ordinary Spears?

If they are weaker, do we know the exact differences, or is this closely guarded info?

Pikes appear to be more effective than Spears, but what’s actually going on behind the scenes that causes this?

Finally, whets the difference between a Short_Pike and a Long_Pike, and also what’s the difference between a Short_Pike and a Spear? (What are the effects of Short_pike in other words).

Long_pike and short_pike were used in RTW to define the length of the phalanx-capable spears (if the unit didn't have the phalanx formation, those were thus redundant). As their names might suggest, they simply made the spears shorter or longer than normal (a Seleucid phalanx having longer spears than a Greek phalanx shows this in action). As one would expect, the only units that use long_pike also have the phalanx formation (or the M2TW version of it). What is sort of interesting is that all units that have the phalanx formation also have long_pikes.
But I digress. Short answer; I assume it's the same as in RTW and simply regulates the length of the pike/spear in a phalanx (or equivalent) formation.

The pike main attribute is news to me, I hadn't even noticed it until now. All units with the pike attribute are phalanxes, though all phalanxes do not have the pike attribute.

The spear attribute was used in RTW to give a unit a bonus against cavalry and possibly a penalty against infantry, I don't remember exactly. I assume light_spear (which I don't remember from RTW) does something similar. How either relate to spear_bonus X, I'm not sure. It was introduced in the BI expansion as I recall. I would guess there's some redundancy there, but to what extent is beyond me.
Other than that, I don't know.