docs: fundamentals section

docs/docs/fundamentals/core-concepts.md

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 # Core concepts
 
-<!-- TODO: write content for this page -->
+You've built an editor. Before going on, it's worth understanding the few
+ideas the whole library is built on. They explain why the API looks the way it
+does and help you understand further chapters better.
+
+## The input is uncontrolled
+
+`EnrichedTextInput` does not take its content from a prop and does not push
+every keystroke back into React state. It owns its content on the native side
+and you talk to it through a `ref`.
+
+This is deliberate. Rich text changes constantly — every character, selection
+move and style toggle — and round-tripping all of that through JavaScript state
+would be extremely slow and open to a possible de-synchronization of those states.
+Keeping it native makes the editor fast and stable.
+
+In practice this means:
+
+- To **change** the content or formatting, call a method on the ref, e.g. `ref.current?.toggleBold()`, `ref.current?.setValue(html)`, or `ref.current?.setLink(...)`.
+- To **observe** changes to the content or formatting, listen to events such as `onChangeState`, `onChangeHtml`, or `onChangeSelection`.
+
+You never set a `value` prop and re-render to make an edit happen.
+
+## HTML is the source of truth
+
+The editor's content is HTML. `setValue` and `defaultValue` seeds it with an HTML string,
+`getHTML` reads the current content back, and `onChangeHtml` streams it as it
+changes. What you store and what you render is a string of HTML.
+
+The library uses a fixed set of standard and custom tags, so the output is
+predictable and portable. [Supported tags](/fundamentals/html-format-and-supported-tags)
+lists exactly what it produces and accepts.
+
+:::caution
+
+Sanitizing HTML is your responsibility. The library doesn't guarantee safe HTML, so
+sanitize anything you persist, render elsewhere, or accept from untrusted
+sources.
+
+:::
+
+## Normalization
+
+HTML can be messy. Whether users paste rich text from applications like Google Docs or Microsoft Word, or you inject external HTML via `defaultValue`, `setValue`, or pass it directly as `children` into `EnrichedText`, the markup often contains additional wrapper elements, inline styles, and structural quirks that may not match the HTML structure expected by the library..
+
+To handle this, both components provide a `useHtmlNormalizer` prop that normalizes incoming HTML. The normalizer cleans and restructures the input into the predictable format the library relies on (e.g., it maps `<strong>` to `<b>`, unwraps `<div>` containers into `<p>` tags, and strips unsupported tags). The `useHtmlNormalizer` prop defaults to `true`.
+
+All supported and canonical tags are listed in [Supported tags](/fundamentals/html-format-and-supported-tags).
+
+## Two components, one HTML format
+
+The library is split into an editor and a viewer:
+
+- **`EnrichedTextInput`** — the interactive editor from the previous page.
+- **`EnrichedText`** — a read-only display component that renders the input's
+  HTML.
+
+The HTML format that both components expect is identical, what allows you to integrate them seamlessly. A common setup edits in `EnrichedTextInput`, stores the `getHTML` output, and later displays it with `EnrichedText`.
+
+## The style state model
+
+Not every style can be combined with every other. For example, a paragraph can't be both a heading and a list item, code blocks don't support inline formatting such as bold or italic. The editor tracks this and reports it through `onChangeState`, which gives each style three booleans:
+
+- **`isActive`** — the style is applied at the current selection. Use it to
+  highlight a toolbar button.
+- **`isBlocking`** — another active style forbids this one entirely, so toggling
+  it would do nothing. For example bold is blocked inside a code block. Use it
+  to disable a button.
+- **`isConflicting`** — this style would replace an active one if toggled on.
+  For example switching a blockquote paragraph to a heading removes the
+  blockquote. Use it to hint that the toggle is a swap, not an addition.
+
+Driving your toolbar from these three flags keeps the UI honest: buttons light
+up and grey out according to the editor's state.
+
+For the comprehensive list of which styles block or conflict with each other, see
+[Supported tags](/fundamentals/html-format-and-supported-tags).

docs/docs/fundamentals/getting-started.md

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 sidebar_position: 1
 ---
 
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
 # Getting started
 
-<!-- TODO: write content for this page -->
+The goal of the _Fundamentals_ section is to get you from an empty project to a
+working rich text editor and to give you the mental model you need to build on
+your own. Let's dive in.
+
+## What is React Native Enriched HTML?
+
+React Native Enriched HTML is a rich text solution for React Native built by
+[Software Mansion](https://swmansion.com/). It supports iOS, Android and Web.
+
+It ships two fully native components: `EnrichedTextInput`, a rich text editor
+that styles text live as you type, and `EnrichedText`, a read-only display component that
+renders the input's output. Both speak HTML — the input
+produces it, the display consumes it.
+
+Not only does this library allow you to apply basic rich text styles you know well,
+like *bold* or _italic_, but also provides more powerful tools like `mentions`, something
+you will learn more about in the next chapters.
+
+## Prerequisites
+
+The library works only with the
+[React Native New Architecture (Fabric)](https://reactnative.dev/architecture/landing-page).
+It's enabled by default on recent React Native versions; if your app still runs
+the old architecture you'll need to switch before installing.
+
+For the exact React Native versions we support, see
+[Compatibility](/misc/compatibility).
+
+## Installation
+
+### Bare React Native
+
+Install the package:
+
+<Tabs groupId="package-managers">
+  <TabItem value="npm" label="NPM">
+    ```bash
+    npm install react-native-enriched-html
+    ```
+  </TabItem>
+
+  <TabItem value="yarn" label="YARN">
+    ```bash
+    yarn add react-native-enriched-html
+    ```
+  </TabItem>
+</Tabs>
+
+The library contains native code, so rebuild your app after installing. On iOS,
+install the pods first:
+
+```sh
+cd ios && bundler install && bundler exec pod install
+```
+
+### Expo
+
+Install with the Expo CLI so the correct version is picked for your SDK:
+
+```sh
+npx expo install react-native-enriched-html
+```
+
+Then regenerate the native projects:
+
+```sh
+npx expo prebuild
+```
+
+:::note
+
+The library needs native code, so it won't run in Expo Go. Use a
+[development build](https://docs.expo.dev/develop/development-builds/introduction/)
+instead.
+
+:::
+
+### Web
+
+Install the package:
+
+<Tabs groupId="package-managers">
+  <TabItem value="npm" label="NPM">
+    ```bash
+    npm install react-native-enriched-html
+    ```
+  </TabItem>
+
+  <TabItem value="yarn" label="YARN">
+    ```bash
+    yarn add react-native-enriched-html
+    ```
+  </TabItem>
+</Tabs>
+
+The shipped components share the React Native's API, minus the functionalities a
+browser can't provide. See the _Web support_ guide for what's covered.
+
+## Nightly builds
+
+To try features before they land in a stable release, install the nightly
+build:
+
+<Tabs groupId="package-managers">
+  <TabItem value="npm" label="NPM">
+    ```bash
+    npm install react-native-enriched-html@nightly
+    ```
+  </TabItem>
+
+  <TabItem value="yarn" label="YARN">
+    ```bash
+    yarn add react-native-enriched-html@nightly
+    ```
+  </TabItem>
+</Tabs>
+
+Nightlies are published to npm automatically and may contain breaking changes.
+
+---
+
+You're set up. Next, let's [build your first editor](/fundamentals/your-first-editor).

docs/docs/fundamentals/html-format-and-supported-tags.md

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 # HTML format and supported tags
 
-<!-- TODO: write content for this page -->
+The editor works with a fixed set of standard and custom HTML tags — it both
+produces them in its output and accepts them as input. This page is the
+reference for that set.
+
+Styles fall into two groups: **inline** tags that wrap a range of characters,
+and **paragraph** tags that apply to whole lines. Not all of them combine
+freely, and there are two kinds of restriction:
+
+- **Conflicting** — toggling a style that conflicts with an active one replaces
+  it. Toggling `<h2>` on a `<blockquote>` paragraph removes the blockquote and
+  applies the heading.
+- **Blocking** — a blocked style can't be toggled at all while the blocking
+  style is active. `<b>` is blocked inside `<codeblock>`, so bold can't be
+  applied there.
+
+Both show up in the [`onChangeState`](/fundamentals/core-concepts#the-style-state-model) payload as
+`isConflicting` and `isBlocking`.
+
+## Inline tags
+
+| Style         | HTML tag    | Conflicts with               | Blocked by             |
+| ------------- | ----------- | ---------------------------- | ---------------------- |
+| Bold          | `<b>`       | --                           | `<codeblock>`          |
+| Italic        | `<i>`       | --                           | `<codeblock>`          |
+| Underline     | `<u>`       | --                           | `<codeblock>`          |
+| Strikethrough | `<s>`       | --                           | `<codeblock>`          |
+| Inline code   | `<code>`    | `<a>`, `<mention>`           | `<codeblock>`, `<img>` |
+| Link          | `<a>`       | `<code>`, `<a>`, `<mention>` | `<codeblock>`, `<img>` |
+| Mention       | `<mention>` | `<code>`, `<a>`              | `<codeblock>`, `<img>` |
+| Image         | `<img>`     | `<a>`, `<mention>`           | `<code>`               |
+
+:::note
+
+Headings also block bold when `bold: true` is set on the heading in the
+`htmlStyle` prop. The heading already renders as bold, so toggling bold on top
+of it is redundant and therefore blocked.
+
+:::
+
+## Paragraph tags
+
+Only one paragraph-level style can be active per paragraph — they all conflict
+with each other.
+
+Some paragraph styles are containers that wrap each line inside them with an
+**inner content tag**. Each line of a `<ul>` is wrapped in `<li>`, and each line
+of a `<codeblock>` is wrapped in `<p>`.
+
+| Style          | HTML tag                    | Inner content tag       | Conflicts with                                                                                                                                                        | Blocked by |
+| -------------- | --------------------------- | ----------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------- |
+| Heading 1      | `<h1>`                      | --                      | `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Heading 2      | `<h2>`                      | --                      | `<h1>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Heading 3      | `<h3>`                      | --                      | `<h1>`, `<h2>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Heading 4      | `<h4>`                      | --                      | `<h1>`, `<h2>`, `<h3>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Heading 5      | `<h5>`                      | --                      | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Heading 6      | `<h6>`                      | --                      | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Unordered list | `<ul>`                      | `<li>`                  | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Ordered list   | `<ol>`                      | `<li>`                  | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ul data-type="checkbox">`, `<blockquote>`, `<codeblock>`                                                    | --         |
+| Checkbox list  | `<ul data-type="checkbox">` | `<li>` / `<li checked>` | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<blockquote>`, `<codeblock>`                                                                         | --         |
+| Blockquote     | `<blockquote>`              | `<p>`                   | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<codeblock>`                                                            | --         |
+| Codeblock      | `<codeblock>`               | `<p>`                   | `<h1>`, `<h2>`, `<h3>`, `<h4>`, `<h5>`, `<h6>`, `<b>`, `<u>`, `<i>`, `<s>`, `<ul>`, `<ol>`, `<ul data-type="checkbox">`, `<blockquote>`, `<code>`, `<mention>`, `<a>` | --         |
+
+## Plain and empty paragraphs
+
+A plain line of text with no paragraph style is wrapped in `<p>`. An empty line
+is represented by `<br>`. So a document with a heading, a blank line and a
+paragraph comes out like this:
+
+```html
+<html>
+  <h1>Title</h1>
+  <br>
+  <p>Some body text.</p>
+</html>
+```