You wrap a subtree in <Ctx.Provider value={x}> and inside that subtree add a second <Ctx.Provider value={y}> for the same context. A consumer deep inside the inner provider reads the context. Which value does it get?
<Ctx.Provider value="outer">
<Middle>
<Ctx.Provider value="inner">
<Leaf /> {/* reads Ctx */}
</Ctx.Provider>
</Middle>
</Ctx.Provider>