here,
    and <code>fortify.merMod</code> is defined as a function
    rather than an S3 method, to avoid (1) inducing
    a dependency on <span class="pkg">ggplot2</span> or (2) masking
    methods from <span class="pkg">ggplot2</span>.
    This feature is both experimental and semi-deprecated,
    as the help page for <code>fortify</code> itself says:
    “Rather than using this function, I now recommend using the
      <code>broom</code> package, which implements a much wider range of
      methods. <c