  We draw from Raney duality and generalize the notion of canonical extension
for distributive lattices to the context of frames. This is a generalization
because for distributive lattices we are in the context of coherent spaces,
whereas frames represent arbitrary spaces. We introduce Raney extensions of
frames, pairs $(L,C)$ where $C$ is a coframe, $L\subseteq C$ is a frame that
meet-generates it, and the inclusion $L\subseteq C$ preserves the frame
operations as well as the strongly exact meets. We think of these as being
algebraic versions of the embedding $\Omega(X)\subseteq \mathcal{U}(X)$ of a
frame of opens into a lattice of saturated sets (upper sets in the
specialization order). We show that a frame may have several Raney extensions,
and all satisfy a generalization of the properties of density and compactness
from the theory of canonical extensions. We show that every frame $L$ has the
largest and the smallest Raney extension, and that these are, respectively, the
coframe of fitted sublocales $\mathsf{S}_{\mathfrak{o}}(L)$ and the opposite of
the frame $\mathsf{S}_{\mathfrak{c}}(L)$ of joins of closed sublocales. We thus
show that these structures have universal properties which are dual of one
another. For Raney extensions $(L,C)$ and $(M,D)$, we characterize the frame
morphisms $f:L\to M$ which can be extended to a morphism of Raney extensions.
We apply this result to obtain a characterization of morphisms of frames
$f:L\to M$ which can be lifted to frame morphisms
$\mathsf{S}_{\mathfrak{c}}(L)\to \mathsf{S}_{\mathfrak{c}}(M)$. We also show
that the canonical extension of a locally compact frame is the free Raney
extension over it such that it is algebraic (generated by its compact
elements). We give a characterization of sobriety and of strict sobriety based
on a variation of the compactness property of the extension
$(\Omega(X),\mathcal{U}(X))$.
