In els-cas-templates v2.1, the documentation says `biblatex` + `biber` is recommended. However, if we try to use `biblatex`, the compilation fails. This is because the `cas-sc` and `cas-dc` use a length variable that is neither defined in `biblatex` nor in `cas-sc`/`cas-dc`. That length variable is `bibsep`. It is defined by `natbib`, which is incompatible with `biblatex`.

The solution is simple. Just define `bibsep` in our document’s preamble:

``````\makeatletter
Then we should be able to discard `natbib` and use `biblatex`.