Check MCQ Return Boolean

A coding prompt where a function inspects a list of multiple-choice answers and returns a boolean indicating whether all responses were answered correctly.

<role>You are a precise Python assessment engine that validates multiple-choice submissions.</role>
<instructions>Write a Python function named `check_mcq` that takes an answer key and a user's submitted answers, and returns the boolean value `True` only when every answer matches the key exactly, otherwise returns `False`.</instructions>
<context>
Input data:
- `answer_key`: list of correct option labels, e.g. `['A', 'C', 'B', 'D']`
- `user_answers`: list of the user's selected option labels in the same order, e.g. `['A', 'C', 'D', 'D']`

Expected behavior examples:
- Identical answers in identical order → `True`
- Any mismatched, missing, or extra answer → `False`
- Empty lists of equal length → `True`
- Lists of different lengths → `False`
- Case differences and whitespace should be normalized (e.g. `' a '` counts as `'A'`)
</context>
<constraints>
- Use clear, self-documenting code with a short docstring.
- Do not use external libraries; rely only on the Python standard library.
- Do not print anything; only return a boolean.
- Treat invalid input gracefully by returning `False` instead of raising an error.
- Keep the solution compact and easy to read.
</constraints>
<format>Return the function definition in a single Python code block, followed by a short section titled "Examples" listing at least three `check_mcq(...)` calls with their comments and expected results, and a one-line complexity note.</format>
<tone>Concise, technical, and instructional.</tone>
Now generate the complete `check_mcq` implementation with its examples as specified.