The reserved words in R's parser are
..2 etc, which are used to refer to
arguments passed down from a calling function. See the
Introduction to R
manual for usage of these syntactic elements,
and dotsMethods for their use in formal methods.
Reserved words outside quotes are always parsed to be
references to the objects linked to in the ‘Description’, and
hence they are not allowed as syntactic names (see
make.names). They are allowed as non-syntactic
names, e.g. inside backtick quotes.