Options of lmerSummary. Any other key is a RangeError (R's lmerTest ignores unknown arguments with a warning).
Optional
The denominator degrees of freedom: "Satterthwaite" (default; with df and p-values) or "lme4" (lme4's table: estimates, standard errors and t values only).
"Satterthwaite"
"lme4"
Options of lmerSummary. Any other key is a RangeError (R's lmerTest ignores unknown arguments with a warning).