parses formulas to creates model matrices
MMeM_terms(fml, data, factor_X)a two-sided linear formula object describing both the fixed-effects and random-effects parts of the model, with the response on the left of a ~ operator. For univariate response, put variable name directly; for multivariate responses combine variables using concatenate operator, for example, for bivariate responses, c(var1, var2). The predictor terms are separated by + operators, on the right. Random-effects terms are distinguished by vertical bars '|' separating expressions for design matrices from grouping factors.
data frame containing the variables named in formula.
(logical) indicating whether predictor is a factor or continuous. By default is TRUE