# `Grammar.Source`
[🔗](https://github.com/joetjen/ichor_runtime/blob/v0.2.0/lib/grammar/source.ex#L1)

The very first, Reader-adjacent stage in front of the Tokenizer:
confirms `input` is valid UTF-8 before any char-level matcher --
built on Elixir binary pattern matching against `::utf8` codepoints --
ever touches it. Malformed input left unchecked doesn't fail cleanly:
it crashes a compiled matcher with a `MatchError` partway through
tokenizing, deep inside either backend, instead of surfacing as an
ordinary `Ichor.Error`.

Shared by both backends (`Grammar.VM.parse/3`/`run_sequence/4` call
this directly; `Grammar.Native`'s generated `tokenize/2` calls it too)
since, like `Grammar.Lexer`, this is pure data validation with nothing
grammar-specific to compile.

# `validate`

```elixir
@spec validate(String.t()) :: {:ok, String.t()} | {:error, Ichor.Error.t()}
```

Returns `input` unchanged if it's valid UTF-8, or an `Ichor.Error` (`stage: :lexer`) otherwise.

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