cos-all-limited.1.2: An 'all' model group must appear in a particle with {min occurs} = {max occurs} = 1, and that particle must be part of a pair which constitutes the {content type} of a complex type definition.

An all model group must appear in the particle with minOccurs=maxOccurs=1. That particle must be part of the pair configuring the content type of a complex type definition.