如何将变量从隔离范围指令传递给子节点？

I have two isolated scope directives. Ideally I like both to work independently and not require any custom templates. The first directive is going to be page scroll watcher, when it hits a certain point I want it to trigger an update in the other directive. Is it possible for a child directive to watch a variable in the parent directive? I have two isolated scope directives. Ideally I