Write a Python function named caesar that satisfies the following specifications:

• It takes the plaintext as a mandatory argument. Assume the value of this argument will be a string.

• It takes the shift as an optional argument. If unspecified, use 13 as a default.

• It converts the plaintext to upper case using the upper() method of strings.

• It returns the requested ciphertext.

• It contains a docstring with the following sections:

  Adescriptionofthepurposeofthefunction An Argssection A Returns section