src/main/java/de/digitalcollections/iiif/model/sharedcanvas/Collection.java
public Collection addMember(Resource first, Resource... rest) {
    if (this.members == null) {
      this.members = new ArrayList<>();
      checkMember(first);
      stream(rest).forEach(this::checkMember);
    }
    this.members.addAll(Lists.asList(first, rest));
    return this;
  }
public Collection addMember(Resource first, Resource... rest) {
    if (this.members == null) {
      this.members = new ArrayList<>();
      checkMember(first);
      stream(rest).forEach(this::checkMember);
    }
    this.members.addAll(Lists.asList(first, rest));
    return this;
  }
Adds one or more member resources.
Must be either instances of {@link Manifest} or {@link Collection}.
All {@link Collection} members must have at least one {@link de.digitalcollections.iiif.model.enums.ViewingHint}.

@param first first member
@param rest other members
@return this collection with added members
@throws IllegalArgumentException if at least one member is not a {@link Manifest} or {@link Collection} or is a
{@link Collection} and does not have at least one {@link de.digitalcollections.iiif.model.enums.ViewingHint}