NIF integrates MARL using property nif:opinion from nif:String to marl:Opinion.
But that's declared inverseOf marl:extractedFrom, which in the MARL example points to sioc:Post (not the nif:String content of the post).
So something doesn't mesh here. We could mix sioc and nif properties on the comment URL, but then nif:sourceUrl points to itself...
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