[_lce0]

actually most of the comments seem to imply that whoever wrote that don't fully understand regexp syntax -- or, worst, she expects that whoever read will not

    /{1,3}                        # 1-3 slashes
    |                             #   or
    [a-z0-9%]                     # Single letter or digit or "%";

[GhotiFish]

err... sorry?

https://www.debuggex.com/r/EpocMU_7Fq_B_p9z

edit:

wait, I thought about it for a second and I see what you meant. You're not saying it's wrong, you're saying it's obvious.

I wasn't sure if it was obvious because I wasn't sure if {1,3} was supposed to be {1-3} and there was a mistake in the expression, or if there was some kind of unexpected error in the [a-z0-9%] expression.

Because even in this simple example, there is room for error.