Tested on epubcheck 4.2.4.

At Standard Ebooks we're trying to add a glossary according to the EPUB Dictionaries and Glossaries 1.0 spec.

In the manifest file, we add two items:

<item href="glossary-search-key-map.xml" id="glossary-search-key-map.xml" media-type="application/vnd.epub.search-key-map+xml" properties="search-key-map glossary"/>
<item href="text/glossary.xhtml" id="glossary.xhtml" media-type="application/xhtml+xml" properties="glossary"/>

According to the spec, we should be able to add the glossary property both to the search key map file to to indicate that the file applies to a glossary, and to the XHTML content document file to indicate that it contains the actual glossary.

However epubcheck outputs:

ERROR(OPF-015): /path/to/glossary.xhtml(-1,-1): The property 'glossary' should not be declared in the OPF file.

It seems to allow glossary for the search key map, but not for the XHTML file.