Under Value section for attr:
For the extractor, the value of the attribute matched,
or \code{NULL} if no exact match is found and no or more
^^^^^^^^^^
than one partial match is found.
R version 2.7.2 (2008-08-25)
-- and --
<https://svn.r-project.org/R/trunk/src/library/base/man/attr.Rd>
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SIGSIG -- signature too long (core dumped)