Data ordinarily flows down, from parent to child. The `bind:` directive allows data to flow the other way, from child to parent.
The general syntax is `bind:property={expression}`, where `expression` is an _lvalue_ (i.e. a variable or an object property). When the expression is an identifier with the same name as the property, we can omit the expression — in other words these are equivalent:
The general syntax is `bind:property={expression}`, where `expression` is an _value_ (i.e. a variable or an object property). When the expression is an identifier with the same name as the property, we can omit the expression — in other words these are equivalent: