Eval and the enclos argument

Hi all,

I'm trying to understand the default value of the enclos argument of eval:

  enclos = if(is.list(envir) || is.pairlist(envir)) parent.frame()
else baseenv()

Why isn't it just

  enclos = parent.frame()

given that enclos is only meaningful (given my reading of the
documentation) when envir is not an environment already.

Hadley