Hmm... perhaps you think I didn't read the documentation you linked to? I did, twice, but that didn't get me very far.

Then you seem to have a real problem reading the documentation. Read the first paragraph below $?, and especially its last sentence. This is the first paragraph:

The status returned by the last pipe close, backtick (``) command, successful call to wait() or waitpid(), or from the system() operator. This is just the 16-bit status word returned by the traditional Unix wait() system call (or else is made up to look like it). Thus, the exit value of the subprocess is really ($? >> 8), and $? & 127 gives which signal, if any, the process died from, and $? & 128 reports whether there was a core dump.

What part of it don't you understand?

Alexander