US 6,322,901 was a battle tested patent - having been through litigation and Patent Office re-examinations, but as we have learned, the PTAB will forge ahead and take down claims if well-challenged. The claims at issue related to what are know as "quantum dots." One particular issue in the case surrounded the Broadest Reasonable Interpretation (BRI) of what seems like a simple list of alternatives.
Namely, some claims required that "the coated nanocrystal emits light in a narrow spectral range selected from blue light, green light, yellow light, orange light, or red light." Many in the field would refer to this as a Markush group. Markush groups are normally written as something "selected from the group consisting of A, B, and C." MPEP 2173.05(h). The slight difference of using "and" versus "or" was cited by the PTAB as confirming that a broader construction was required than that argued for by the Patent Owner.
As background, the typical Markush group is used for the purpose of listing alternatives in the claim, without using the word "or" since some examiners just don't like the word "or" in a claim. However, some attorneys, always aiming to avoid unintentional narrowing, switch to using Markush language plus "or." The reason is that sometimes claims using this type of language are construed as meaning that all of the listed options have to be available, even if in the end only one is actually selected.
Here, the Patent Owner actually attempted to use the "or" language as a way to argue for a narrower construction (to avoid prior art). This approach was not successful, but makes clear that even the slightest wording choice can change the intended claim scope into something different under the BRI.