<brandlogo>
The <brandlogo> element specifies a logo image for a publisher,
project, or site brand. Place it in <docinfo>; the
source attribute gives the image file, and url can make the logo link
to an external site.
Syntax
Examples
<pretext>
<docinfo>
<brandlogo
source="images/pretext-logo.png"
url="https://pretextbook.org"
/>
</docinfo>
<book>
...
</book>
</docinfo>