Attribute groups

Defining Attribute groups in requirements files requires an attribute to be added with data-type attribute-group, and a type to define the attributes to be included in the group. That type should never be created directly, but is just a definition for what attributes should be included in the group.

# The "container" object
type test:type:type-with-file-group
   attribute test:attribute:files-with-info

attribute test:attribute:files-with-info as FilesWithInfo
   title: Files with info
   search-name: files-with-info
   qualifier std:qualifier:null
   data-type attribute-group
   group-type test:type:group-of-attributes

# This type defines the attributes to be included in the "group"
# Only attributes and labels are relevant
type test:type:group-of-attributes as TestGroup
   title: Test group
   behaviour hide-from-browse
   attribute std:attribute:file
   attribute dc:attribute:author
   attribute std:attribute:notes
   label-applicable std:label:common
   label-default std:label:common