[Doitsu]

Originally Posted by FrustratedReader

linear="no" has no practical use as it doesn't work on the majority of epub readers and apps, even though this is in the epub2 spec.

Actually, the epub2 spec states:

For each itemref, the publication author may specify the optional linear attribute to designate whether the associated OPS Content Document is primary (linear="yes", which is the default when linear is not present) or auxiliary (linear="no".) [...]
Reading Systems are not required to differentiate between primary and auxiliary content, and for the requirements and recommendations given in this section may consider all OPS Content Documents in spine to be primary, regardless of the value of the linear attribute.