Deligne's purity conjecture for constructible l-adic sheaves

Let $X$ be a scheme over $\mathbf{F}_p$, and let $F$ be a constructible $\mathbf{Q}_l$-sheaf on $X$. Purity conjecture. Every constructible $\mathbf{Q}_l$-sheaf on $X$ is mixed.

This is presented as a striking conjecture in the theory of weights of l-adic sheaves. The supplied text does not state its resolution or provide enough information to determine whether the assertion is intended in a more precise $\iota$-mixed formulation.