 by the
element size in bytes. A read access loads the element value and
<a href="#convert_tolua">converts it to a Lua object</a>. A write
access <a href="#convert_fromlua">converts a Lua object to the element
type</a> and stores the converted value to the element. An error is
raised if the element size is undefined or a write access to a
constant element is attempted.</li>

<li><b>Dereferencing a <tt>struct</tt>/<tt>union</tt> field</b>: a
cdata <tt>struct</tt>/<tt>union</tt> or a pointer to a
<tt>struct</