> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sdk.fdo.alexvwan.me/llms.txt
> Use this file to discover all available pages before exploring further.

# Basics

> Understand the fundamental SDK rules before building larger plugins.

# Basics

## The One Rule That Matters Most

Do not mix backend runtime and iframe UI runtime.

Backend runtime is for:

* `init()`
* handlers
* stores
* logging
* diagnostics
* privileged action setup

Iframe UI runtime is for:

* DOM access
* browser event handling
* `window.createBackendReq(...)`
* host-injected UI libraries

## What `render()` Really Returns

`render()` returns UI source for the FDO iframe pipeline.

It is not:

* arbitrary host DOM HTML injection
* direct React component source you control in the host app

The safest mental model is:

* JSX-compatible UI source for a sandboxed iframe render pipeline

## DOM Helper Rule

If you use SDK DOM helpers and expect styling to work, wrap the final output with `renderHTML(...)`.

Without that, helper-generated classes may exist but their CSS will not be emitted.

## Safe Authoring Rules

* prefer JSX-safe tags like `<br />`
* avoid raw `<style>` blocks in `render()`
* escape literal braces in code samples
* do not pass untrusted raw strings into generic DOM helper children
* use `DOMText` helpers for user-provided text

## Metadata Rule

`metadata.icon` must be a valid BlueprintJS v6 icon name.

## Storage Rule

Do not call `PluginRegistry.useStore(...)` in class field initializers.

Acquire stores lazily or inside `init()` / handlers.

## Read Next

* [Quickstart](/getting-started/quickstart)
* [Learning Path](/getting-started/learning-path)
* [Runtime Model](/guides/runtime-model)