fixup! Update docs

docs/guide.md

@@ -3,6 +3,7 @@
 **Table of contents**
 
 - [Tree](#tree)
+  - [Layouts](#layouts)
   - [Normalization](#normalization)
   - [Floating windows](#floating-windows)
 - [Default keybindings](#default-keybindings)
@@ -15,10 +16,35 @@
 - [Multiple displays](#multiple-displays)
 
 ## Tree
-TODO DOCUMENTATION. This section is yet to be written, for now you can refer to https://i3wm.org/docs/userguide.html#tree
+
+AeroSpace stores all windows and wrapping layout containers in a tree. AeroSpace tree tiling model is [inspired by
+i3](https://i3wm.org/docs/userguide.html#tree).
+
+- Each workspace contains its own single root node
+- Each non-leaf node can contain arbitrary number of children nodes
+- Windows are the only possible leaf nodes. Windows contain zero children nodes
+- Every non-leaf node has two properties: layout and orientation. 2 possible layouts and 2 possible orientations combined produce
+  [4 possible layouts](#layouts) in total.
+
+When we say "layout of the window", we refer to the layout of the window's parent.
+
+It's easier to understand tree tiling model by looking at examples
+
+![](./.assets/h_list.png)
+![](./.assets/tree.png)
+
+### Layouts
+
+AeroSpace provides 4 possible layouts:
+- horizontal list (in i3, it's called "horizontal split")
+- vertical list (in i3, it's called "vertical split")
+- horizontal accordion (analog of i3's "tabbed layout")
+- vertical accordion (analog of i3's "stacked layout")
 
 ### Normalization
-TODO DOCUMENTATION
+
+By default, AeroSpace does two types of normalizations to the tree:
+- Containers that have only one child are "flattened".
 
 ### Floating windows
 TODO DOCUMENTATION
@@ -27,6 +53,7 @@ Normally, floating windows are not part of the tiling tree. But it's not the cas
 perspective, floating windows are part of the tree. 
 
 ## Default keybindings
+
 TODO DOCUMENTATION the idea behind default keybindings
 
 ## Configuring AeroSpace
@@ -35,8 +62,8 @@ AeroSpace will read config file from `~/.aerospace.toml`. Please see the followi
 - The default config contains all possible keys with comments: [default-config.toml](../config-examples/default-config.toml)
 - i3 like config: [i3-like-config-example.toml](../config-examples/i3-like-config-example.toml)
 
-AeroSpace uses TOML format for the config. TOML is a popular format with open specification. TOML is easy to read, and it supports
-comments. See [TOML site for more info](https://toml.io/en/)
+AeroSpace uses TOML format for the config. TOML is easy to read, and it supports comments. See [TOML site for more
+info](https://toml.io/en/)
 
 ### Binding modes
 TODO DOCUMENTATION
@@ -57,7 +84,18 @@ TODO DOCUMENTATION
 Enable 'Group windows by application'
 
 ### A note on 'Displays have separate Spaces'
-TODO DOCUMENTATION
+
+AeroSpace doesn't care about `System Settings -> Desktop & Dock -> Displays have separate Spaces` setting. It works equally good
+whether this option is turned off or on.
+
+Overview of 'Displays have separate Spaces'
+
+|                                                             | 'Displays have separate Spaces' is enabled | 'Displays have separate Spaces' is disabled |   |   |
+|-------------------------------------------------------------|--------------------------------------------|---------------------------------------------|---|---|
+| When the first display is in fullscreen                     | 😊 Second monitor operates independently   | 😔 Second monitor is black screen           |   |   |
+| Is it possible to place a window on the border of monitors? | 😔 No                                      | 😊 Yes                                      |   |   |
+| macOS status bar ...                                        | ... is displayed on both monitors          | ... is displayed only on main monitor       |   |   |
+
 
 ## Multiple displays
 TODO DOCUMENTATION