r-callable function.</p>
<p>A typical model has the form <code>response ~ terms</code> where
  <code>response</code> is the (numeric) response data frame and <code>terms</code>
  is a series of terms which specifies a linear predictor for
  <code>response</code>. A typical form for <code>terms</code> is <code>.</code>,
  which is shorthand for "all variables" in <code>data</code>. If <code>.</code> is
  used, <code>data</code> must also be provided. If specific species
  (variables) are required then <code>