| Reserved {base} | R Documentation |
The reserved words in R's parser are
NULL
NaN
NA_real_
NA_character_
... and ..1, ..2 etc, which are used to refer to
arguments passed down from an enclosing function.
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.