(! classification                                         ## ! starts the DSL and 'classification' is the name of tag category which allows us doing an arbitrary number of tagging.
    (@ (HASH (: "name" holding.atype.name)                ## @ is the rule. The first argument (The whole HASH block) is the tag.
             (: "order" holding.atype.order))             ## In this case, we have a hash of name/order object as our tag.
       true                                               ## This is the condition. As we want to stick on the ctype (atype here), we set to true.
       ($ (@ (HASH (: "name"  holding.artifact.stype)     ## $ is child rules. And the rest is similar as @ has the same meaning as above.
                   (: "order" holding.artifact.stype))
             (NOT (EMPTY? holding.artifact.stype))))))    ## We are not interested in the null/empty stypes.