PHP Manual:
Language->Operators->Error Control Operators
"The @-operator works only on expressions. A simple rule of thumb is: if you can take
the value of something, you can prepend the @ operator to it. For instance, you can
prepend it to variables, function and include() calls, constants, and so forth. You cannot
prepend it to function or class definitions, or conditional structures such as if and
foreach, and so forth."
-Cursed