[DOC] "expr1 ?: expr1" is a shortcut for: "expr1 ? expr1 : expr2" as
exists in gcc and discussed some time back. Note that this is not
an implementation ifsetor($var, default). While ifsetor would not
generate any message for non existing variables or array indices
the ternary shortcut does. Also the ternary shortcut does a boolean
evaluation rather then checking for isset(). That way ther ternary
shortcut can work on any expression while ifsetor can only work on
variables. Also to be silent one has do do: "@$expr1 ?: $expr2".
