Syntax	Value	Direction	Evaluated	Aliased?	Optional?
foo: @	Value of DOM attribute	Out -> In	Out	No	No
foo: @?	Value of DOM attribute	Out -> In	Out	No	Yes
bar: @foo	Value of DOM attribute	Out -> In	Out	Yes	No
bar: @?foo	Value of DOM attribute	Out -> In	Out	Yes	Yes
foo: =	Expression passed by attribute	Out <-> In	In	No	No
foo: =?	Expression passed by attribute	Out <-> In	In	No	Yes
bar: =foo	Expression passed by attribute	Out <-> In	In	Yes	No
bar: =?foo	Expression passed by attribute	Out <-> In	In	Yes	Yes
foo: <	Expression passed by attribute	Out -> In	In	No	No
foo: <?	Expression passed by attribute	Out -> In	In	No	Yes
bar: <foo	Expression passed by attribute	Out -> In	In	Yes	No
bar: <?foo	Expression passed by attribute	Out -> In	In	Yes	Yes
foo: &	Value passed by attribute	Out <- In	Out	No	No
foo: &?	Value passed by attribute	Out <- In	Out	No	Yes
bar: &foo	Value passed by attribute	Out <- In	Out	Yes	No
bar: &?foo	Value passed by attribute	Out <- In	Out	Yes	Yes