I hope you're doing well. I've been working on a PHP project and I came across a function called `cal_to_jd()`. I tried to understand how it works, but I'm a bit confused.
I would really appreciate it if someone could explain the `cal_to_jd()` function to me and provide an example to better grasp its usage. I want to understand how this function can be used effectively in PHP.
Thanks in advance!