Return the names of all the built-in objects. These are fetched directly from the symbol table of the R interpreter.
builtins(internal = FALSE)a logical indicating whether only ‘internal’
    functions (which can be called via .Internal) should
    be returned.
A character vector.
builtins() returns an unsorted list of the objects in the
  symbol table, that is all the objects in the base environment.
  These are the built-in objects plus any that have been added
  subsequently when the base package was loaded.  It is less confusing
  to use ls(baseenv(), all = TRUE).
builtins(TRUE) returns an unsorted list of the names of internal
  functions, that is those which can be accessed as
  .Internal(foo(args ...)) for foo in the list.