The function would be to keep or drop a specified number of the highest or lowest numbers.

As an example:
4d6kh3 / 4d6dl1
Roll four 6-sided dice, keep the highest 3 rolls; or to the same effect, Roll four 6-sided dice, drop the lowest roll.

2 things for this: "10-again" and "Count Successes"

10-again: If the maximum number for that die is rolled, keep it and add one more roll. Also referred to as "exploding".
Example: 3d10! --> 1,6,10 (and since this 10 is the maximum of 1d10, keep it and add one more roll), 7

Count Successes: Instead of adding all numbers above a result together, count how many of them there are.
Example: Using our previous example, we are looking for how many numbers are equal to or higher than 8.
3d10!>=8 --> 1,6,10,8 = 2 (counted, not added)