title: What is the difference between src and tgt in nn.Transformer for PyTorch?
body: <p>From the docs it says to create a transformer model like this:</p>
  <pre><code>transformer_model = nn.Transformer(nhead=16, num_encoder_layers=12)
  src = torch.rand((10, 32, 512))
  tgt = torch.rand((20, 32, 512)) # What is tgt??
  out = transformer_model(src, tgt) 
  </code></pre>
  <p>What is tgt mean't to be? Should tgt be the same as the src?</p>