PAC 2 Error
Non-standard structure type [X] is neither mapped to a standard structure type nor to another non-standard structure type
PDF/UA > Logical Structure > Role mapping > Role mapping of non-standard structure types
Matterhorn Protocol Checkpoint 02-002: The mapping of one or more non-standard types is semantically inappropriate.
In the Tags pane in Acrobat Pro, click the Options icon at the top left and select “Edit Role Map”. In the Role Map dialog, click the New Item button. In the Add Role dialog, map the non-standard structure type to an appropriate standard structure type.
Video version of this suggestion: