# Composed-page books

> A walk through the Sandbox with a school textbook made of composed pages: build a page template, fill it from the Markdown, label a map, translate the page, fix what does not fit and select on the page and in the text

- HTML version: https://postext.dev/en/docs/composed-page-books
- Last updated: 2026-10-17
- Reading time: 12 min
- Other languages: [es](https://postext.dev/es/docs/composed-page-books.md), [ca](https://postext.dev/ca/docs/composed-page-books.md), [de](https://postext.dev/de/docs/composed-page-books.md), [fr](https://postext.dev/fr/docs/composed-page-books.md), [it](https://postext.dev/it/docs/composed-page-books.md), [pt](https://postext.dev/pt/docs/composed-page-books.md), [zh](https://postext.dev/zh/docs/composed-page-books.md), [ja](https://postext.dev/ja/docs/composed-page-books.md), [ar](https://postext.dev/ar/docs/composed-page-books.md)

## In short

This page teaches, step by step, how to make a page of a school textbook in the Sandbox, the page with a title band, a text and coloured boxes. You start from a finished example book and add one more page to it. First you draw the page as a template, then you pour the text into it from the Markdown, then you name the places on a map and translate the page into another language. At the end you see what to do when a text is too long for its box and how to jump between the page and its text.

**You build one page of a textbook from a template, fill it with text from the Markdown, label a map, translate the page and fix what does not fit.**

A page of a school textbook is a set of boxes: a title band, a text, a box for a definition, a box for an activity, a map. Postext lays such a page out from a **page template** that holds the boxes (its frames), and the Markdown only says which words go in which frame. This page walks through the whole job in the Sandbox, on a book that already exists, and adds one page to it. The reference pages say what each field and each line of Markdown does; here you do each thing once, in order, and see what it changes: [Composed pages](https://postext.dev/en/docs/composed-pages.md) for the Markdown, [Configuration › Composed pages](https://postext.dev/en/docs/configuration-composed-pages.md) for the template, [Sandbox: composed pages](https://postext.dev/en/docs/sandbox-composed-pages.md) for the screens.

You need a browser and nothing else. Every step happens in the Sandbox, and what you change stays in your browser.

## 1. Open the book

The book is *Our river*, a unit of a Year 3 textbook that the [Cookbook](https://postext.dev/en/cookbook/children-textbook-pages.md) publishes as recipe Nº 156. The river, the towns and the pictures are invented for it. It has nine pages, with a painted map across two facing ones, and it comes in Spanish, Catalan and English.

[Open it in the Sandbox](https://postext.dev/en/sandbox.md#recipe=children-textbook-pages&lang=en). The first visit adds it to **Books** as one of your own books, so you can change it freely; with `lang=es` or `lang=ca` in the link you get the other editions. If you come back to the same link later, the Sandbox asks whether to open your copy or to replace it with the published one.

Two things to know before you touch anything:

- The bar above the preview has a switch with **Content** and **Design**. In Content mode you edit words, in the **Text** panel or on the page. In Design mode you edit page templates and styles, and the text is read only. **Alt+Shift+M** (**⌥⇧M** on a Mac) switches between them.
- The **Text** panel shows one chapter of Markdown. Each composed page is a block that starts with `::::page{template="…"}` and ends with four colons. Click some words on a page in the preview and the caret goes to them in the Markdown.

## 2. Make a page template

The new page will be a review page: a title band, a short text under it and two boxes, one to recall what was learned and one to try. It needs a template with four frames.

1. Switch to **Design** and open the **Design** panel on the left. Choose **Page & columns**, then **Page templates**. The list shows each template of the book with a drawing of its frames.
2. Press **New**. A template called *New template* opens. Give it the **ID** `review` (what the Markdown will name) and the **Name** `Review page` (what this panel shows). The ID takes lowercase letters, digits and dashes.
3. The template starts with one frame, `text`, that **Takes the page's loose text**. Make it the title band: **Name (slot)**: `title`; **Box style**: `portada`, the blue band the book already uses for its titles; switch **Takes the page's loose text** off; **Takes the first heading**: *Level 1*, so that this frame receives the page's first `#` heading.
4. Press **Add frame**. The new frame opens below the list of frames. **Name (slot)**: `text`, and switch **Takes the page's loose text** on: whatever the page writes outside a frame goes here.
5. Add a frame. **Name (slot)**: `remember`. **Box style**: `dato-campo`, a green box with a tab. **Smallest height**: 30 mm, so that the box keeps a good size when its text is short.
6. Add a last frame. **Name (slot)**: `try`. **Box style**: `actividad-sol`. **Smallest height**: 30 mm.
7. In `text`, `remember` and `try` set **Width** to *Up to the edge* and **Height** to *Its content*: they then fill the width of the page and are as tall as their text.
8. Under **Groups** press **Add group**. Name it `column`, leave it *Stacked* and set **Space between frames** to 6 mm. Under **Members, in page order** tick the four frames. The group keeps them in the order of the list of frames, so the title is first. A group lays its frames one under the other and moves the ones below when a frame grows, so a longer text in the first box pushes the second box down instead of running over it.

![The Design panel on Page templates with the Review page template: its four frames and its group, and the same frames drawn with dashed outlines on the page.](https://postext.dev/docs-shots/en/template.webp)

*The template: four frames and one group. On the page, the dashed boxes are the frames and the green labels say how each one is sized.*

The template has no words in it. Nothing you set says what the title is or what the boxes contain; the box style gives a frame its look, the group its order. There are other ways to the same template. In Design mode you can draw a frame on an empty spot of a composed page with the mouse and move or resize the frames you have (see [Sandbox: composed pages](https://postext.dev/en/docs/sandbox-composed-pages.md#page-templates)); **Duplicate** copies a template to change it; **Save layout as template** turns a composed page you like into a new template.

## 3. Fill the page from the Markdown

1. Switch to **Content**, open the **Text** panel and press **Ctrl+End** (**Cmd+↓** on a Mac) to go to the end of the chapter.
2. Press **Composed page** in the toolbar of the Text panel. A picker lists the page templates of the book, each drawn as its empty frames. Choose *Review page*.
3. The Sandbox writes the page for you, one empty frame per slot, and selects the word `title` of the heading. Type the title over it.

```md
::::page{template="review"}
# Check what you have learned

A river changes as it runs from the mountains to the sea. Read the boxes, then answer them in your own words.

:::frame{slot="remember" label="Remember"}
A spring gives a trickle, streams join into a river, and the river widens as it nears the sea.
:::

:::frame{slot="try" label="Try it"}
Draw a river from its spring to the sea. Write the names of the three courses on your drawing.
:::
::::
```

The heading goes to the frame that takes level 1, the paragraph that follows it to the frame that takes the loose text, and each `:::frame` to the frame of its `slot`. The `label` is the words on the tab of a box. The page is on the canvas as page 10, after the nine of the unit: a composed page always starts a new page.

![The Text panel with the Markdown of the new page, and the finished page beside it with a blue title, a paragraph and two boxes with tabs.](https://postext.dev/docs-shots/en/fill.webp)

*The page in the Markdown and on the canvas.*

Notice what the Markdown does not say: no position, no size, no colour. Those belong to the template, and the same Markdown laid out with another template would look different.

## 4. Label the map

Pages 6 and 7 hold a painted map across the spread. Its words are not part of the picture. Each name on it is a line of the Markdown, inside the `:::figure` of the map:

```md
:::figure{resource="mapa" slot="mapa"}
::label[Spring]{at="nacimiento"}
::label[Molinar]{at="molinar"}
::label[Lower course]{at="bajo"}
:::
```

`at` names an **anchor**: a point of the picture, defined once in the picture's resource and shared by every language. To add the stone bridge of Molinar:

1. In the Text panel go to the map's figure (search for `at="bajo"`) and add a line under the last label: `::label[Stone bridge]{at="bridge"}`.
2. Open **Checks**. The list has a *Label at an unknown anchor* entry for page 6: the picture has no anchor called `bridge`. Press the pin button on the entry, *Place the anchor bridge on the picture*.
3. A dialog shows the map with the anchors it has. The name `bridge` is picked under *Labels without an anchor*. Click the picture where the bridge stands.
4. Set the **Label style** of the new anchor to `pueblo`, the style of the towns, and press **Save**.

![The Anchors dialog: the map with its points, the new anchor named bridge selected and its label style field.](https://postext.dev/docs-shots/en/anchor.webp)

*The new anchor is a click on the picture; its label style makes it look like the names of the towns.*

![The map across pages 6 and 7 with the new label Stone bridge on the bridge, beside the labels of the towns.](https://postext.dev/docs-shots/en/map.webp)

*The label is set at the point you clicked, in the book's own fonts.*

The word *Stone bridge* is Markdown; the point is part of the picture. When you translate the page, the same anchor gets another word.

## 5. Translate the page

A translation is the same template with other words. The Sandbox has two ways to hold it. A book can carry several languages at once, as a `.postext` file with an edition for each, and then the bar above the canvas switches between them and the Checks panel reads all of them (see [Editions of a book](https://postext.dev/en/docs/sandbox-previews.md#editions-of-a-book)). The simpler way, which needs no file, is a copy of the book in the other language:

1. Open **Books**, press **⋯** on your book and choose **Duplicate**, or press **New** and choose **Copy of the open book**. Open the copy. It has the same name as the original: give it another one with **Rename…** in the same menu.
2. In the **Design** panel open **Writing system** and, under **Language and direction**, set the **Document language**. Hyphenation, quotation marks and the words the engine writes itself (such as *Continued* at the cut of a box) follow it.
3. In the **Text** panel translate the words and leave the rest.

| You translate | You leave as it is |
| --- | --- |
| The text of headings, paragraphs and lists | The four colons, the word `page` and the `template="…"` of the fence |
| The `label="…"` of a frame | The `slot="…"` of a frame |
| The text in the brackets of `::label[…]`, `::alt[…]` and `::caption[…]` | The `at="…"` of a label and the `resource="…"` of a figure |

The pictures, the anchors, the boxes and their colours come along with the copy and need no work. A copy of the review page in Spanish looks like this:

```md
::::page{template="review"}
# Repasa lo aprendido

Un río cambia mientras baja de las montañas al mar. Lee los recuadros y respóndelos con tus propias palabras.

:::frame{slot="remember" label="Recuerda"}
Un manantial da un hilo de agua, los arroyos se unen en un río y el río se ensancha al acercarse al mar.
:::

:::frame{slot="try" label="Inténtalo"}
Dibuja un río desde su manantial hasta el mar. Escribe en tu dibujo el nombre de los tres cursos.
:::
::::
```

![The copy of the book in the other language: the Text panel with the translated page and the page on the canvas with the translated title, text and tabs.](https://postext.dev/docs-shots/en/translate.webp)

*The translated page: the template is the same, the words are not.*

## 6. Review what does not fit

Words differ in length from one language to the next, and a box that held the English text may not hold the Spanish one. The Checks panel finds those frames. To see one, paste three or four more paragraphs of any text into the `remember` frame of the translated page, so that it holds more than the page has room for.

The page now shows the frame outlined in red with a band under its foot that says how much is missing (*26 mm short*). In **Checks**, under *Composed pages*, the entry *Text does not fit its frame* says what the layout tried before giving up (more room from the frames around, then smaller text) and lists the ways out as buttons:

- *let the text shrink to 82.5 %* lets the text of this frame go down to that size. It suits a few lines too many.
- *continue it on the next page* sends what does not fit to a page added after this one. It suits a longer text.
- *cut about 495 characters* changes nothing. It selects the text of the frame and tells you how much to cut.

A button that changes the template (every page set with it) asks first, naming the setting. Press **Change it**. The page is laid out again, the box ends with the word of the cut (*Continúa*) and the rest runs on at the head of an added page. **Cmd/Ctrl+Z** takes the change back. **Reflow**, in the bar above the canvas, opens *What moved and why*: the frames whose size or place the layout changed to fit their content, with the reason in words.

![The Checks panel with the entry Text does not fit its frame and three buttons with ways out, and the page with its first box outlined in red and a band saying 26 mm short.](https://postext.dev/docs-shots/en/checks.webp)

*A frame that does not fit, and the fixes the layout worked out for it.*

## 7. Select on the page and in the text

The page and its Markdown follow each other.

- **From the page to the text.** Click on the words of a frame: the caret goes to that paragraph in the Text panel, and a path under the preview names where you are (*Page 10 › column › try › paragraph 1*). In Design mode the same click picks the frame for the template editor instead.
- **From the text to the page.** Put the caret in a paragraph and the frame that holds it and the paragraph itself are outlined on the page, and the same path says where they are.
- **From a check.** Click an entry of the Checks panel and the Sandbox takes you to the page, picks the frame and puts the caret at its text. In a book with several editions it switches to the edition that has the problem.
- **On the tab of a box.** Double-click it and a field opens over it for the `label`. Enter keeps the change and Esc leaves it.

![The page with the second box outlined in orange, and the Text panel showing the selected frame in its Markdown.](https://postext.dev/docs-shots/en/select.webp)

*A click on the page puts the caret in its Markdown, and the path under the preview says which frame it is.*

## Where to go next

- [Moving a book to composed pages](https://postext.dev/en/docs/migrating-to-composed-pages.md): a book that keeps the text of its pages in its styles can have it moved into the Markdown.
- [Composed pages](https://postext.dev/en/docs/composed-pages.md): every attribute of the page fence, the figure and the label lines, how a page is set and every warning with its fix.
- [Configuration › Composed pages](https://postext.dev/en/docs/configuration-composed-pages.md): every field of a template, a frame and a group, inheritance and spreads.
- [Sandbox: composed pages](https://postext.dev/en/docs/sandbox-composed-pages.md): the screens for templates, frame styles, checks in every edition and fixes.