The CAFC has recently focused attention on the use of functional claim language—that is, claim language that describes what an element does, rather than describing what the element is. A recent IPR showed how functional claiming can play out at the PTAB, where it is often the case that neither the petitioner nor the patent owner wants the claims to be construed as employing “means-plus-function” language. For the petitioner, such an interpretation would make it more difficult to show invalidity. For the patent owner, such an interpretation could substantially narrow the scope of the claim and have a significant downstream impact on the patent owner’s ability to show infringement. But the PTAB may have its own ideas about how to interpret the claims.