Function bind_state 

pub fn bind_state<T>(
    child: impl IntoUiNode,
    source: impl IntoVar<T>,
    state: impl IntoVar<T>,
) -> UiNode
where
    T: VarValue,

Helper for declaring state properties that are controlled by a variable.

On init the state variable is set to source and bound to it, you can use this to create state properties that map from a context variable or to create composite properties that merge other state properties.