R's df: Satterthwaite's degrees of freedom.
R's Estimate: l'β̂.
Whether the rows were tested jointly: always false here.
OptionallowerR's lower: the lower limit of the confidence interval of the estimate (unless confint: false).
R's messages (none so far).
R's Pr(>|t|).
R's Std. Error.
R's t value: (estimate − rhs) / stdError.
OptionalupperR's upper: the upper limit of the confidence interval (unless confint: false).
R's warnings (about the Hessian's eigenvalues).
Result of lmerContest with
joint: false: one t-test per row of L.