def contains(self, pat, case=True, na=np.nan):
pass<EOL>
Return whether each value contains `pat`.

In this case, we are illustrating how to use sections, even
if the example is simple enough and does not require them.

Parameters
----------
pat : str
    Pattern to check for within each element.
case : bool, default True
    Whether check should be done with case sensitivity.
na : object, default np.nan
    Fill value for missing data.

Examples
--------
>>> s = pd.Series(['Antelope', 'Lion', 'Zebra', np.nan])
>>> s.str.contains(pat='a')
0    False
1    False
2     True
3      NaN
dtype: object

**Case sensitivity**

With `case_sensitive` set to `False` we can match `a` with both
`a` and `A`:

>>> s.str.contains(pat='a', case=False)
0     True
1    False
2     True
3      NaN
dtype: object

**Missing values**

We can fill missing values in the output using the `na` parameter:

>>> s.str.contains(pat='a', na=False)
0    False
1    False
2     True
3    False
dtype: bool