# `Expresso.Overlay.Verifier`
[🔗](https://github.com/rellen/expresso/blob/main/lib/expresso/overlay/verifier.ex#L1)

The check of the overlays

`Expresso.VerifierTransformer` runs it after the other transformers, one
time for each deck module at compile time, so an error stops the compile.
It calls `Expresso.Overlay.Check.slide/1` for each slide. An error from the
check becomes a `Spark.Error.DslError` with the path of the slide. It then
calls `Expresso.Overlay.Properties.registered_state/2`, which refuses a state
that takes the name of a property that the theme registers.

# `verify`

```elixir
@spec verify(map()) :: :ok | {:error, Spark.Error.DslError.t()}
```

Check the steps and the states of each slide of the deck

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*Consult [api-reference.md](api-reference.md) for complete listing*