A decision that has perhaps not yet received the recognition it
deserves is the U.S. Court of Appeals for the Federal Circuit's
June en banc decision Williamson v. At Home Bondholder.
It deals with a fairly arcane bit of patent law—"means plus
function" claim drafting. As the terms suggests, it describes one
mode of drafting a patent "claim" (such as the numbered paragraphs
at the end of a utility patent that describe the "invention"
protected by the patent. A "means plus function" claim typically
reads as follows: "a means to" or "means for" followed by a
description of the function achieved.
This format has long been used by patent drafters. The drawback,
however, is that once a patent claim is considered to be in that
format, Section 112, paragraph 6 of the Patent Act and its
requirements for what must also be spelled out in the patent in
order for that claim to be valid kick in.
Read the article here.