Warlocks benefit in a specific way from prestige classes that have "+1 spellcasting level of existing arcane spellcasting class" or "+1 level of existing spellcasting class" as a level advancement benefit. A warlock taking levels in such a prestige class does not gain any of his class abilities, but he does gain an increase in caster level when using his invocation and increased damage with his eldritch blast. Levels of prestige classes that provide +1 level of spellcasting effectively stack with the warlock's level to determine eldritch blast damage (treat his combined class level as his warlock level when looking at table 1-1: The Warlock) to determine eldritch blast damage and eldritch blast caster level (half his total class level from his warlock and the prestige class that grants him an increased spellcasting level). [Errata'd out.] A warlock also gains new invocations known at these prestige class levels as though he had gained a level in the warlock class.