JSON Pointer
The standard syntax manni meta uses to name the field an error is about.
The standard is RFC 6901. A
pointer like /tags/0 means “the first item of the tags array”. An empty
pointer, shown as (root) in pretty output, means the document as a whole.
That is most often a required field that’s missing entirely. Pointers appear in
error output and in the instancePath field of JSON output.