title: What is the meaning of outputs_collections in slim.arg_scope?
body: <p>Saw this in the alexne.py in slim, could not find the documentation for this. Was wondering what is a collection? I am guessing its a type of container, in this case it would be for output nodes? And was wondering what is the purpose of this, as opposed to using the name of the outputs. </p>
  
  <pre><code>    with tf.variable_scope(scope, 'alexnet_v2', [inputs]) as sc:
  
      end_points_collection = sc.name + '_end_points'
      with slim.arg_scope([slim.conv2d, slim.fully_connected, slim.max_pool2d],
                          outputs_collections=[end_points_collection]):
          net = slim.conv2d(inputs, 64, [11,11], 4, padding = 'VALID', scope ='conv1')
  </code></pre>