563 U.S. 421, 438, 131 S.Ct. 1866, 179 L.Ed.2d 843 (2011). Nonetheless, the District Court and the Plan have cited to the language in the Summary Plan Description (“SPD”) as the language of the Plan. We, too, adopt this approach. See US Airways, Inc. v. McCutchen, 569 U.S. 88, 133 S.Ct. 1537, 1543 n.1, 185 L.Ed.2d 654 (2013) ("Because everyone in this case has treated the language from the summary description as though it came from the plan, we do so as well.”). Moreover, insofar as McLaughlin and J.J.M. now contend that the SPD was not "designated a plan document” and so cannot control here, McLaughlin Reply Br. 1, we deem this argument forfeited because it is raised solely in the reply brief. See Laborers' Int'l Union of N. Am. v. Foster Wheeler Corp., 26 F.3d 375, 398 (3d Cir. 1994) (<HOLDING>). 4 . We have considered McLaughlin's and
holding an argument not raised in opening brief is waived holding that a party waives an argument that it raises in the background section of its brief but not in the argument section holding argument waived for failure to raise it in opening brief holding that argument not raised in opening brief is waived holding that an argument is not preserved unless a party raises it in its opening brief