def sum_even_fibonaccis(limit):
    """Find the sum of all even terms in the Fibonacci sequence whose values
    do not exceed the provided limit.
    """
    # Fibonacci seed values are 0 and 1.
    previous, current, even_fibonacci_sum = 0, 1, 0

    while previous + current <= limit:
        # This is a memoized calculation; a matrix calculation would be faster.
        previous, current = current, previous + current

        # Check if the current term in the sequence is even.
        if current % 2 == 0:
            even_fibonacci_sum += current

    return even_fibonacci_sum