2.2.10 [W3C-EPUB3] Section 4.4.2.3.2. Allowed values

C0013: The rendition:orientation property is not supported and is ignored

The specification states:

 › 4.4.2.3.2 Allowed values
  
 The following values are defined for use with the rendition:orientation property:

EdgeHTML Mode

The rendition:orientation property is not supported and is ignored.