bag on the side

from Jargon File (4.4.4, 14 Aug 2003)
bag on the side
 n.

   [prob. originally related to a colostomy bag] An extension to an
   established hack that is supposed to add some functionality to the
   original. Usually derogatory, implying that the original was being
   overextended and should have been thrown away, and the new product is
   ugly, inelegant, or bloated. Also v. phrase, "to hang a bag on the
   side [of]". "C++? That's just a bag on the side of C ...." "They want
   me to hang a bag on the side of the accounting system."
    
from The Free On-line Dictionary of Computing (8 July 2008)
bag on the side

   An extension to an established hack that is supposed to add
   some functionality to the original.  Usually derogatory,
   implying that the original was being overextended and should
   have been thrown away, and the new product is ugly, inelegant,
   or bloated.  Also "to hang a bag on the side [of]".  "C++?
   That's just a bag on the side of C."  "They want me to hang a
   bag on the side of the accounting system."
    

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