2020-1 EPUBs with PNG cover images (cover.png) do not validate

[keyvantextalk]

2020-1 guidelines, under Image File Naming and Directory Structure, state that the cover image should be cover.png or cover.jpg.

An exception to this is the cover image, which should be named simply cover.png or cover.jpg.

And under Cover:

The front cover, when available, must be captured as a .jpg or .png image file and given the name cover.jpg/png.

But the validation rules produce the following error when validating a 2020 EPUB with cover.png:

[opf15b] The image with property value 'cover-image' must have the filename 'cover.jpg': (<item href="images/cover.png" id="coverimg" media-type="image/png" properties="cover-image">)

[martinpub]

Hi @keyvantextalk! OK, this seems like a bug then. We did open up for PNGs with 2020-1 (only JPEG images were allowed in 2015-1), and there should not be a difference when it comes to cover images, so the rule should be updated to follow the 2020-1 text.

[keyvantextalk]

Thanks @martinpub! Okay, will wait for rule update then 👍

[keyvantextalk]

Fixed by #558