title: What does it mean that backpropagation will happen into labels?
body: <p>I received an warning today, it said</p>
  
  <blockquote>
    <p>softmax_cross_entropy_with_logits (from tensorflow.python.ops.nn_ops) is deprecated and will be removed in a future version.
    Instructions for updating:</p>
    
    <p>Future major versions of TensorFlow will allow gradients to flow
    into the labels input on backprop by default.</p>
  </blockquote>
  
  <p>and I then checked <code>tf.nn.softmax_cross_entropy_with_logits_v2</code> as it suggested, and found something below</p>
  
  <blockquote>
    <p>Backpropagation will happen into both logits and labels. To disallow backpropagation into labels, pass label tensors through a stop_gradients before feeding it to this function.</p>
  </blockquote>
  
  <p>I don't quite understand what it means that backpropagation will happen into labels, aren't the labels set to be constants?</p>