The Federal Circuit, in HD Silicon Solutions LLC v. Microchip Technology, Inc., No. 2023-1397 (Fed. Cir. Feb. 6, 2025), reiterated that extrinsic evidence may be used only to assist in the proper understanding of the disputed limitation; it may not be used to vary, contradict, expand, or limit the claim language from how it is defined, even by implication, in the specification or file history.