// Swings per second
As fast as you can click?



// Invulnerability
maxHurtResistance = 20
// It looks like you can get hurt again before the half way point if it does more damage than the previous attack
// It doesn't reset the invuln. timer though



// Knockback on attack
knockback = 0
if ( target instanceof EntityLiving )
{
    // ...
    knockback += Knockback enchantment level
}
if ( sprinting )
{
    knockback += 1
}

if ( total damage > 0 )
{
    // ...
    // If entity's NBT tag "Invulnerable" is true, there will be no knockback
    // No knockback for the enderdragon
    // No knockback for the wither from arrows in the second stage
    // Probably more exceptions as well
    if ( entity can be knocked back for this damage source )
    {
        x velocity += attacker direction * knockback * 0.5f
        y velocity += 0.1
        z velocity += attacker direction * knockback * 0.5f

        x velocity *= 0.6;
        z velocity *= 0.6;
    }
    // ...
}