message: Defined structure in module overview
diff: @@ -19,6 +19,10 @@ This module can perform operations on nested structures. A nested structure is a
  Python sequence, tuple (including `namedtuple`), or dict that can contain
  further sequences, tuples, and dicts.
  +Structures are scalar, or tuple or dict or list of constructed scalars and/or
  +other tuples/lists, or a scalar object. Note, numpy arrays are considered
  +scalars.
  +
  attr.s decorated classes (http://www.attrs.org) are also supported, in the
  same way as `namedtuple`.
  @@ -243,11 +247,8 @@ def is_nested(seq):
  def flatten(structure, expand_composites=False):
  """Returns a flat list from a given nested structure.
  - If nest is not a structure (which can be a scalar, or
  - tuple or dict or list of constructed scalars and/or other tuples/lists,
  - or a scalar object. Note, numpy arrays are considered scalars.), tuple
  - (or a namedtuple), dict, or an attrs class, then returns a single-element
  - list:
  + If nest is not a structure , tuple (or a namedtuple), dict, or an attrs class,
  + then returns a single-element list:
  [nest].
  In the case of dict instances, the sequence consists of the values, sorted by
  @@ -263,9 +264,7 @@ def flatten(structure, expand_composites=False):
  running.
  Args:
  - structure: an arbitrarily nested structure which can be a scalar, or
  - tuple or dict or list of constructed scalars and/or other tuples/lists, or
  - a scalar object. Note, numpy arrays are considered scalars.
  + structure: an arbitrarily nested structure.
  expand_composites: If true, then composite tensors such as tf.SparseTensor
  and tf.RaggedTensor are expanded into their component tensors.
  @@ -310,14 +309,8 @@ def assert_same_structure(nest1, nest2, check_types=True,
  ```
  Args:
  - nest1: an arbitrarily nested structure which can be a scalar, or
  - tuple or dict or list of constructed scalars and/or other
  - tuples/lists, or a scalar object. Note, numpy arrays are considered
  - scalars.
  - nest2: an arbitrarily nested structure which can be a scalar, or
  - tuple or dict or list of constructed scalars and/or other
  - tuples/lists, or a scalar object. Note, numpy arrays are considered
  - scalars.
  + nest1: an arbitrarily nested structure.
  + nest2: an arbitrarily nested structure.
  check_types: if `True` (default) types of sequences are checked as well,
  including the keys of dictionaries. If set to `False`, for example a
  list and a tuple of objects will look the same if they have the same
  