peek_vars() returns the vector of names of the variables
currently available for selection.
peek_data() returns the whole input vector (only available with
eval_select()).
Read the Get started for
examples of how to create selection helpers with peek_vars().
The variable names in a selection context are registered
automatically by eval_select() and eval_rename() for the
duration of the evaluation. peek_vars() is the glue that connects
selection helpers to the current selection
context.
peek_vars(..., fn = NULL)
peek_data(..., fn = NULL)