Some projects will provide opportunities for you to earn extra credits. Extra-credit tests will be included in the tests released - you can see whether your code passes the extra-credit tests or not. These tests reward students who go beyond the requirements of the project and implement extra functionality.
Apart from P1, each project will have 10 extra-credit points, evenly divided among sub-parts. For example, P2A has 5 extra-credit points.
The sum of all extra credit points (a total of 40 points) will count towards a max of 5% of the total grade. The final grade is capped at 100% - if you have 98% from your projects and exams, and full extra credit, your final grade will be 100% and not 103%.
Finally, as the name implies, this is extra credit: do not be worried if you did not pass extra-credit tests. You can get a perfect grade without doing any extra-credit tests.