What Part of "And" Don't You Understand?
The USPTO recently identified several decisions as informative. While not binding, an informative decision provides guidance for patent applicants, examiners and the PTAB. Of note for patent applicants is Ex parte Jung, where claims recited "at least one of A and B." Applicants often use this expression to mean "either A or B." In fact, that's how the examiner in this case interpreted it.
But the PTAB construed this expression to mean "at least one of A and at least one of B." In reaching its conclusion, the Board relied on CAFC precedent and on the ordinary meaning of "and." The PTAB took this position in spite of the fact that the specification did not support such a conjunctive limitation (A and B), and only supported the disjunctive one (A or B). The PTAB distinguished other cases that adopted the disjunctive interpretation (A or B) because, in this case, the specification did not "compel" the such interpretation (A or B), which would be contrary to the ordinary meaning of "and."
Pushing the reasoning to its logical end, the PTAB issued a rejection for failure to meet the written description requirement for (A and B).
Update: on August 7, 2018, the PTAB de-designated this decision as being “informative” because it did not “reflect new or changed policies with respect to claim construction. … The case remains a routine decision of the Board.”