R: did you know ``comment(.) and comment(.) <- ...''

[Martin Maechler]

I'm doing some systematic investigations about which functions are
<primitive> in R (and which of these should be changed to .Internal(...))...

I just discovered :

> x <- 1:10
> comment(x)
NULL
> comment(x) <- "x is just a vector"
> x
 [1]  1  2  3  4  5  6  7  8  9 10
> attributes(x)
$comment
[1] "x is just a vector"

> comment(x)
[1] "x is just a vector"

----------
Who of you (besides Ross?)  did know this feature.

"comment" is an *INVISIBLE* (for printing) 
attribute you can give to anything, including  functions and data.frames.

Any volunteer for writing a Rdoc file "comment.Rd" (for `?comment' to
work)?

Martin
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