Explained in [https://nim-lang.github.io/Nim/manual.html#templates-hygiene-in-templates](https://nim-lang.github.io/Nim/manual.html#templates-hygiene-in-templates)
Any variables declared in a template annotated with {.inject.} will be
accessible in the scope where the template is called, effectively injecting the
variable from the template into the location of the call.
