How does being attuned/repelled/denied affect casting level?
Some spells are attuned to one or more spell classes (such as wounding, summoning, fire and so on). The player can likewise be attuned to some of these classes, giving a bonus, or repelled to them, giving a malus, or denied to them, making her unable to cast the spell at all. The skill level is the level of the skill that the spell uses (e.g. summoning or sorcery). When attuned, the bonus is up to 16 levels, but never higher than the skill level itself, i.e. at level 2, the bonus is 4, at level 5, the bonus is 10 and at level 50, the bonus is 16. When repelled, the malus is 16 levels always. These are added (or subtracted) to the skill level when checking whether the player can cast the spell and when calculating the effective casting level. The effect on strength is as if the minimum spell level is lower (when attuned) or higher (when repelled), and the strength will increase the same as without any attunement.
