[R] Subclassing lm

[rlee@fpcc.net]

I'd trying to subclass the "lm" class to produce a "mylm" class whose
instances behave like lm objects (are accepted by methods like summary.lm)
but have additional data or slots of my own design.

For starters:

setClass("mylm", "lm")

produces the somewhat cryptic:
 Warning message:
Old-style (``S3'') class "mylm" supplied as a superclass of "mylm", but no
automatic conversion will be peformed for S3 classes in:
.validDataPartClass(cl, name)

What does this imply?

-Rob