sfref is an attribute that we use to resolve dynamic links. Its value is [Provider]Guid - this shows the data provider and the item ID. When the content is saved or edited we call LinkParser.ResoveLinks and pass the entire HTML of the content item. We check for this attribute and its value. Then we set the proper href if the item is found.Generally you should not change the sfref, otherwise the item url will not be resolved properly and when you rename the content item( image, document etc) this will break the link.
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