The major title of a work, excluding label and any subtitles.
This element is only used for the top-level <book> and <book-part-wrapper> elements, and is found inside the <book-title-group> as part of the book metadata.
<!ELEMENT book-title (#PCDATA %book-title-elements;)* >
(#PCDATA | email | ext-link | uri | inline-supplementary-material | related-article | related-object | hr | bold | fixed-case | italic | monospace | overline | overline-start | overline-end | roman | sans-serif | sc | strike | underline | underline-start | underline-end | ruby | alternatives | inline-graphic | private-char | chem-struct | inline-formula | tex-math | mml:math | abbrev | index-term | index-term-range-end | milestone-end | milestone-start | named-content | styled-content | fn | target | xref | sub | sup | x | break)*
Any combination of:
<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>