Well, let's analyze it with the help of java.util.regex.Pattern:
- (?<=\\?)l2=.*?& (1)
- |
- \\?l2=.*?$ (2)
- |
- &l2=.*?& (3)
- |
- &l2=.*?$ (4)
So you have part 1 or part 2 or part 3 or part 4.
Part 1 starts with a positive lookbehind of a single ?. So it's "l2=" preceded by (but not part of the match) a single ?, and followed by anything until the first & (the .*? is reluctant, stopping whenever the & is found).
Part 2 is similar: a single ? (this time part of the match), followed by "l2=", followed by anything until the end of the line ($).
I'm sure you can work out parts 3 and 4 by following the same way of thinking.