# Core Concepts

## Shell

A Shell is a titled container — think of it as a heading that can actually hold things.

- Each Shell has a title.
- Inside a Shell, you can add blocks or nest other Shells.
- When Shells nest, hierarchy forms automatically, just like H1 → H2 → H3 in traditional documents.

## Creating a Shell

To create a Shell on canvas, press `S` or click the Shell icon in the **Select panel** at the bottom center. Then click anywhere on the canvas.

In Docs view, or to create a Shell inside another Shell, use the slash (`/`) command. The available Shell options will appear based on your current hierarchy level — simply select one to create it.

## Wrapping with Shell

Select multiple Shells or block groups, and a floating toolbar appears. Click `Wrap with Shell` to combine them into a single new Shell. (`⌘` \+ `Option` \+ `Enter`, or `Ctrl` \+ `Alt` \+ `Enter` on Windows)

This enables **bottom-up thinking** — start with scattered pieces, then group them into structured concepts as patterns emerge.

## Nesting Shells

Drag one Shell into another to create a nested hierarchy. The dropped Shell becomes a child of the target Shell, moving one level deeper (e.g., S1 → S2).

## Adding Blocks into a Shell

Drag Block Groups into a Shell to add them as its content. Position them wherever you want inside the Shell.

When Shells are nested, a background and border highlights show which Shell will receive the Blocks.

## Shell Layout Rules

Elements inside a Shell are arranged according to layout rules. Currently, we provide vertical alignment, but we plan to soon allow arranging internal elements in multiple columns.