The TensorBoard UI shows something called a "Reference edge" as distinct from a data flow (Tensor) edge:
What distinguishes the former from the latter?
The documentation says that "the outgoing operation node can mutate the incoming tensor", but indicates different symbols that don't match the UI, so it's hard to tell what's meant by "incoming" and "outgoing":
For example how does this definition apply to
cs = tf.constant([1,2,3], name='const_share')
vs = tf.Variable([1,2,3], name='var_share')
tf.add(cs, vs, name='opVS1')
tf.add(vs, cs, name='opVS2')
or to
tf.add([4],[3], name='opA')
In both cases it just seems that the reference edge indicates that the value its tail fills the Tensor represented by the edge.