heads down

from Jargon File (4.4.4, 14 Aug 2003)

heads down
 adj.

   Concentrating, usually so heavily and for so long that everything
   outside the focus area is missed. See also {hack mode} and {larval
   stage}, although this mode is hardly confined to fledgling hackers.

from The Free On-line Dictionary of Computing (8 July 2008)

heads down

   [Sun] Concentrating, usually so heavily and for so long that
   everything outside the focus area is missed.  See also {hack
   mode} and {larval stage}, although this mode is hardly
   confined to fledgling hackers.

   [{Jargon File}]

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