# Strata

> Detail bound to one shape on a diagram, opened by clicking that shape.

A stratum is a block of detail attached to one shape. The reader clicks the
shape and the detail opens beside it, with the diagram still on screen.

![blueprint:josh/anatomy-of-a-stratum](https://blueprintr.io/embed/josh/anatomy-of-a-stratum#h=520)

In a long page of prose the reader has to work out which paragraph belongs to
which box. A stratum removes the guess: the detail has exactly one owner, and
the owner is the thing they are already looking at.

## What a stratum holds

A stratum is a set of tabs, and each tab has a kind. One stratum can mix them:
an overview in Rich, the config it describes in Raw, and a Subdiagram that
opens the box up.

| Kind | Holds |
| --- | --- |
| Rich | Markdown, images, embedded diagrams |
| Raw | Code or config, rendered line-numbered |
| Subdiagram | A diagram of its own, in any supported engine |
| Image | A single image, uploaded or linked |
| Embed | An embeddable URL. YouTube and Google Maps links convert automatically |

## Adding one

Right-click the shape and choose **Add Stratum…**. The modal opens already
bound to that shape.

Right-click the same shape later and the item reads **Edit Stratum…**. Shapes
carrying a stratum are marked on the canvas.

> [!TIP]
> A stratum does not have to be created from the shape. The link picker binds
> an existing stratum to any shape on any surface in the blueprint, including
> diagrams embedded inside rich text. See [Linking strata](/foliums/blueprintr-user-guide/strata/linking-strata).

## What readers get

Hovering a marked shape for half a second shows a preview card with the
stratum's name and its opening lines. Clicking opens it in a window that moves
and resizes by its corners, or docks to a panel down the right-hand side at
half the viewport width.

Readers can leave the panel open and work through several strata in turn while
the diagram stays put.

> [!TILES 3]
>
> === [Creating and editing](/foliums/blueprintr-user-guide/strata/creating-and-editing)
>
> The modal, the tabs, and what happens on save.
>
> === [Tab kinds](/foliums/blueprintr-user-guide/strata/tab-kinds)
>
> What each kind renders, and when to use it.
>
> === [Linking strata](/foliums/blueprintr-user-guide/strata/linking-strata)
>
> The picker, the `stratum:` link scheme, and multi-target links.