Model's batch_size field's name does not make sense

[ninesunqian]

In model.py these are some lines

"self.batch_size = tf.size(self.iterator.source_sequence_length) "
.....
"start_tokens = tf.fill([self.batch_size], tgt_sos_id)"
....
" crossent = tf.nn.sparse_softmax_cross_entropy_with_logits(labels=target_output, logits=logits)
target_weights = tf.sequence_mask(self.iterator.target_sequence_length, max_time, dtype=logits.dtype)
.....
loss = tf.reduce_sum(crossent * target_weights) / tf.to_float(self.batch_size)
"

1 self.source_sequence_length is better than self.batch_size.
2 why not loss = tf.reduce_sum(crossent * target_weights) / target_sequence_length ?

Thanks!