A container element for the various title elements that might be used for the book.
<!ELEMENT book-title-group %book-title-group-model; >
(label?, book-title?, subtitle*, trans-title-group*, alt-title*, fn-group?)
The following, in order:
<book dtd-version="1.0">
<book-meta>
<book-id book-id-type="doi">...</book-id>
<book-id book-id-type="other">emdocrin</book-id>
<book-title-group>
<book-title>Endocrinology</book-title>
<subtitle>An Integrated Approach</subtitle>
</book-title-group>
...
</book-meta>
<front-matter>...</front-matter>
<book-body>...</book-body>
<book-back>...</book-back>
</book>