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

# Content type: learning unit

> The published contract for learning units — purpose, tone, required components, title grammar, and copy-paste templates for both forms.

A **learning unit** is one stop in an ordered learning sequence — the "Learn
the OP Stack" track or a per-feature curriculum hub. It gives an existing
page a place in a syllabus: what the learner already knows on arrival, what
this stop adds, and where to go next. Content is linked and framed, never
duplicated.

This page is the contract for the type. A new learning unit is reviewed
against it; cite the relevant section in review instead of re-arguing it.

## Purpose

* Let newcomers progress **linearly** through material that was written to
  be read in any order.
* Add **sequencing context only**: orientation, prerequisites-by-position,
  and a pointer to the next stop.
* Protect the underlying pages: a track that needs a page reworded forks
  nothing — it files an issue against the page itself.

## Composition

A learning unit is a composition, not a fifth quadrant. It has two forms:

* **Framing header** (the default): a short framing block prepended to an
  existing page that serves as a track stop. The page keeps its own
  `diataxis:` value; nothing else about it changes.
* **Standalone unit page** (the exception): a new short page written
  because a sequence needs a stop that no existing page provides (for
  example, a bridging paragraph between two concepts in a curriculum hub).
  It carries the quadrant of what it actually is — usually
  `diataxis: explanation`, or `diataxis: tutorial` for a hands-on stop —
  plus `content-type: learning-unit`.

See [Choose a content type](/op-stack/contribute/choose-a-content-type) for
the explanation-vs-learning-unit decision table.

## Tone

* Welcoming but not chatty; the learner is mid-sequence, so respect their
  momentum.
* Second person, present tense: "you now know…", "this page adds…".
* The frame never editorializes about the underlying page ("this excellent
  guide…") and never summarizes it — a one-line statement of what the stop
  adds is the ceiling.

## Required components

**Framing header** (on an existing page):

1. An `<Info>` block at the top of the page body, below the frontmatter and
   any existing callouts.
2. Inside it, in order: the track name and stop position ("stop N of M"),
   one sentence of arrival context (what the learner knows from previous
   stops), one sentence of what this stop adds, and a link to the next stop
   (or a completion line on the last stop).
3. Nothing else changes on the page: same `diataxis:` value, same content.

**Standalone unit page**:

1. **Frontmatter**: `title`, `description`, `diataxis:` (the quadrant of
   what the page actually is), `content-type: learning-unit`.
2. **The same framing block** as above, so every stop reads uniformly.
3. **A body that earns its existence**: material no existing page owns. If
   an existing page covers it, use a framing header on that page instead.
4. **A forward exit**: the last line links the next stop, or the track
   index on completion.

## Title grammar

* A framing header adds **no title** — the underlying page keeps its own.
* A standalone unit page titles the concept as a plain noun phrase in
  sentence case ("Fault proof economics", "From transactions to blocks").
  Position ("Part 3:", "Lesson 3") never appears in the title — order
  lives in the track's nav group and the framing block, so stops can be
  resequenced without retitling.

## Templates

Framing header — copy onto an existing page that becomes a track stop:

```mdx theme={null}
<Info>
  **<Track name> — stop <N> of <M>.**
  You've <what the previous stops covered>. This page <what this stop
  adds>. When you're done, continue to [<next stop title>](</path/to/next>).
</Info>
```

Standalone unit page:

```mdx theme={null}
---
title: <Concept noun phrase>
description: <One sentence: the concept and what understanding it unlocks.>
diataxis: explanation
content-type: learning-unit
---

<Info>
  **<Track name> — stop <N> of <M>.**
  You've <what the previous stops covered>. This page <what this stop
  adds>. When you're done, continue to [<next stop title>](</path/to/next>).
</Info>

<The concept, at the smallest size that lets the learner continue the
sequence. Link the canonical deep material rather than reproducing it.>

## Next stop

Continue to [<next stop title>](</path/to/next>), where you'll <what comes
next>.
```

## Exemplars

No track is wired yet — the learn track and curriculum hubs consume this
contract when they ship. Calibrate against the pages that would become
stops, and the external patterns:

* [The OP Stack](/op-stack/introduction/op-stack) and the
  [fault proofs explainer](/op-stack/fault-proofs/explainer) — existing
  explanations that would gain a framing header, unchanged otherwise.
* [Bridging your ERC-20 token](/app-developers/tutorials/bridging/cross-dom-bridge-erc20)
  — the shape of a hands-on stop (`diataxis: tutorial`).
* The [Rust Book](https://doc.rust-lang.org/book/) — the cadence this
  type exists to reproduce: strictly ordered chapters, hands-on projects
  spaced through the sequence, depth exiled to reference.