Lock levels for ALTER TABLE

EnterpriseDB reports that our documentation states that ALTER TABLE
takes SHARE UPDATE EXCLUSIVE and ACCESS EXCLUSIVE lock modes.  However,
their testing shows only ACCESS EXCLUSIVE locks.  Is this accurate? 
Have we changed how ALTER TABLE locks but didn't update our docs?
--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +