I don't know if it's calibre or the Modify epub plugin that's inserting these comments in the jacket page.
Quote:
<!--<!==
In addition you can add code to show the values of custom columns here.
The value is available as _column_name and the title as _column_name_label.
For example, if you have a custom column with label #genre, you can add it to
this template with _genre_label and _genre. Note that the # is replaced by an underscore.
-->
<p>--></p>
|
Which results in
always being visible before the book description.
EDIT: It seems to be calibre.