docs: Initial import from localai-website (#1312)

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

docs/content/features/constrained_grammars.md

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+
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+disableToc = false
+title = "✍️ Constrained grammars"
+weight = 6
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+
+The chat endpoint accepts an additional `grammar` parameter which takes a [BNF defined grammar](https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form).
+
+This allows the LLM to constrain the output to a user-defined schema, allowing to generate `JSON`, `YAML`, and everything that can be defined with a BNF grammar.
+
+{{% notice note %}}
+This feature works only with models compatible with the [llama.cpp](https://github.com/ggerganov/llama.cpp) backend (see also [Model compatibility]({{%relref "model-compatibility" %}})). For details on how it works, see the upstream PRs: https://github.com/ggerganov/llama.cpp/pull/1773, https://github.com/ggerganov/llama.cpp/pull/1887
+{{% /notice %}}
+
+## Setup
+
+Follow the setup instructions from the [LocalAI functions]({{%relref "features/openai-functions" %}}) page.
+
+## 💡 Usage example
+
+For example, to constrain the output to either `yes`, `no`:
+
+```bash
+curl http://localhost:8080/v1/chat/completions -H "Content-Type: application/json" -d '{
+  "model": "gpt-4",
+  "messages": [{"role": "user", "content": "Do you like apples?"}],
+  "grammar": "root ::= (\"yes\" | \"no\")"
+}'
+```