This file defines class/kit bonuses or penalties.
It applies a static (i.e., unaffected by level) bonus(-)/penalty(+) to THAC0.
In BG2EE we have:

2DA V1.0 
* 
                MAGE                FIGHTER             CLERIC              THIEF               BARD                PALADIN             DRUID               RANGER              FIGHTER_MAGE        FIGHTER_CLERIC      FIGHTER_THIEF       FIGHTER_MAGE_THIEF  MAGE_THIEF          CLERIC_MAGE         CLERIC_THIEF        FIGHTER_DRUID       FIGHTER_MAGE_CLERIC CLERIC_RANGER       ABJURER             CONJURER            DIVINER             ENCHANTER           ILLUSIONIST         INVOKER             NECROMANCER         TRANSMUTER          BERSERKER           WIZARD_SLAYER       KENSAI              CAVALIER            INQUISITOR          UNDEAD_HUNTER       FERALAN             STALKER             BEASTMASTER         ASSASIN             BOUNTY_HUNTER       SWASHBUCKLER        BLADE               JESTER              SKALD               TOTEMIC_DRUID       SHAPESHIFTER        BEAST_FRIEND        TALOS               HELM                LATHANDER           MONK                BARBARIAN           SORCERER            WILDMAGE            SHADOWDANCER        DWARVEN_DEFENDER    DRAGON_DISCIPLE     DARK_MOON           SUN_SOUL            BLACKGUARD    OHTYR    SHAMAN
BONUS           0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0                   0             0        0