Depends on the type of AE spells.
Most Targeted AE spells where up to 4 targets - Examples, would be the druid lightning line, and the wizard equalents - in short, the quadding spells and similar
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Rain spells where 4 targets pr wave(3 waves).
PBAE Spells unlimited amount of targets. Same goes for most of the non damaging AE spells, druid blind(god i loved that one during arena events, you could hit an entire event with it.), harmony, mezmerisation (still broke here and limited to 4 tgts - i hate you for it), where all unlimited on live.