The _refId is the unique identifier of a list item. Field attributes of List Items, like names, are not necessarily unique, e.g., I can have the same person twice in a list of persons, but they have different _refId. You cannot search for it in the Content Browser or List Item Browser as those are not available in the search index, but you can directly add the refId to the URL e.g. https://demo.picturepark.com/Lists/Products/Tags/5bda1f1bdd7f47a281f0555781e64daf
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