At least as of recent versions of lme4
, this is documented (albeit way down in the details) in ?anova.merMod
(emphasis added):
‘anova’: returns the sequential decomposition of the contributions of fixed-effects terms or, for multiple arguments, model comparison statistics. For objects of class ‘lmerMod’ the default behavior is to refit the models with ML if fitted with ‘REML = TRUE’, this can be controlled via the ‘refit’ argument. See also ‘anova’.