PHP has no built-in debugger.
This is HUGE. The ability to say
perl -d .... and have a fully featured, gdb-like debugger at your command, with absolutely nothing to download or install, is HUGE.
Debugging PHP is an epic pain in the best of circumstances, and it’s all but impossible on a system you don’t control and can’t waste a bunch of time on even if you had permission to install things.
If I’m wrong, please correct me!