High-growth stock valuations elevated, but far from the extremes seen during the dotcom bubble, Bernstein notes. 
Very profitable companies tend to stay very profitable for longer than they did in the past as well.
Buybacks has been the biggest prop to equity demand over the past decade, but ex-tech buybacks are now outpaced by equity issuance.
Effective US corporate tax rates have been declining for three decades, but have fallen further for tech companies.
