3.0rc3: 'os.extsep' gone ... ?

[bMotu]

IDLE 2.6
>>> import os
>>> os.extsep
'.'
running XP this result is fine ... !

IDLE 3.0rc3
>>> import os
>>> os.extsep
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    os.extsep
AttributeError: 'module' object has no attribute 'extsep'

why is this attribute gone in 3.0rc3 ?

where is this documented ?

ciao, motu