[R] How to find where the source code of an R function or package is installed?

[Peng Yu]

I'm wondering where is the source of an R function or a package is.
For example, where is 'attributes'?

> attributes
function (obj)  .Primitive("attributes")

I also do understand what .Primitive mean. Could somebody let me know
how to locate source file in an R installation? Why typing
'attributes' does not give its definition?