When validating a Epub created out of Indesign 2015, I get a validation error from the cover.xhtml file Epub Validation error: "HTML5 DOCTYPE definition within EPUB v2".
The issue is within line 2 of the create cover.html file. Indesign creates the line "<!DOCTYPE html"> when it should be <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">as it does for all other files that are created in the epub document. Please can you fix this error as it will be one less thing that needs manually editing after export.
See image Below:
Moved to InDesign EPUB forum.
This has been reported already to the Adobe developers. Now, we have to wait for a fix and change it manually in the meantime.