http://www.pwg.org/pipermail/ipp/2018/019504.html

Attributes (attribute syntax)
  Keyword Attribute Value				Reference
  -----------------------				---------
printer-state-reasons (type2 keyword)			[PWG5100.9]
  subunit-cooling-down					[HPINC20180214]

Add HP registration of "subunit-cooling-down".
Add HP registration of "subunit-cooling-down".
