A path is a more general substitute for the name of a field or feature that
can be used for flat examples as well as structured data. For example, if
we had data in a protocol buffer:
message Person {
  int age = 1;
  optional string gender = 2;
  repeated Person parent = 3;
}
Thus, here the path {step:["parent", "age"]} in statistics would refer to the
age of a parent, and {step:["parent", "parent", "age"]} would refer to the
age of a grandparent. This allows us to distinguish between the statistics
of parents' ages and grandparents' ages. In general, repeated messages are
to be preferred to linked lists of arbitrary length.
For SequenceExample, if we have a feature list "foo", this is represented
by {step:["##SEQUENCE##", "foo"]}.

Protobuf type tensorflow.metadata.v0.Path