introAfter the head element there may be one
intro element. This is just a way to define a group
of chapter that have no numbering. Chapters inside this element
are delimited in the same way as for the body and
appendix elements.
<intro>
<h1>Introduction to Sgmltexi</h1>
<p>Sgmltexi is a DTD with tools to get Texinfo...</p>
<p>Sgmltexi manage Texinfo nodes automatically,...</p>
</intro>