Explanation:

- The Principle of Estoppel is essentially a rule in law.

- Option 1: The maxim ‘allegans contratia non est audiendus’

- This Latin phrase translates to "he who alleges contradictory things is not to be heard."

- It's a foundational concept related to not allowing someone to backtrack on their statements in legal proceedings.

- Option 2: Rule of evidence

- Estoppel is seen as a rule of evidence, which prevents a party from contradicting what they previously established as true.

- Option 3: Both (A) & (B)

- The principle draws from both the Latin maxim and is applied as a rule of evidence in various legal systems.

- Hence, it is based on both concepts.

- Option 4: None of the above

- This option would mean that neither of the previous reasons applies, which is inaccurate.

Correct Answer: Option 3 — Both (A) & (B)