2.2.4 [W3C-EPUB3] Section 3.4.13. The itemref Element
C0007: No control is provided over the rendering order for non-linear content
The specification states:
› 3.4.13 The itemref Element The child itemref elements of the spine represent a sequential list of Publication Resources (typically EPUB Content Documents). The order of the itemref elements defines the default reading order of the given Rendition of the EPUB Publication. ... The linear attribute may be used to enable Reading Systems to distinguish presentation of body content from supplementary content which might be, for example, presented in a popup window or omitted from an aural rendering. Reading Systems should provide Users the ability to control whether non-linear content is rendered in the default reading order.
No control is provided over the rendering order for non-linear content.