diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -31,11 +31,13 @@ together.
 
 # Requirements
 
-1. Apache-2.0 licence for the project.
-1. Tree based container for placing dashboard elements.
+1. Native support of the UTF-8 encoding.
+1. Simple container management to position the widgets and set their size.
 1. Mouse and keyboard input.
 1. Cross-platform terminal based output.
 1. Unit testing framework for simple and readable tests of dashboard elements.
+1. Tooling to streamline addition of new widgets.
+1. Apache-2.0 licence for the project.
 
 # High-Level design
 
diff --git a/doc/design.md b/doc/design.md
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--- a/doc/design.md
+++ b/doc/design.md
@@ -2,12 +2,154 @@
 
 ## Objective
 
+Develop infrastructure of dashboard widgets. The widgets should support both
+input (mouse and keyboard) and output (display of information to the user).
+
+Fulfill the requirements outlined in the main
+[README](http://github.com/mum4k/termdash).
+
 ## Background
 
+The terminal dashboard allows placement of configurable widgets onto the terminal.
+
+A widget displays some information to the user, e.g. A graph, a chart, a
+progress bar. A widget can receive information from the user in the form of
+events, e.g. Mouse or keyboard input.
+
+The widgets aren't placed onto the terminal directly, instead the terminal is
+organized into containers. Each container can contain either a widget or
+other containers.
+
 ## Overview
 
+The terminal dashboard consists of the following layers:
+
+- Display.
+- Infrastructure.
+- Widgets.
+
+The **display layer** abstracts the display implementation. A real terminal
+implementation is used in production when displaying on the terminal. A fake
+terminal implementation is used in widget unit tests and system tests. Other
+implementations are possible, e.g. Image export. The display layer is private,
+neither the users of this library nor the widgets interact with the display
+directly.
+
+The **infrastructure layer** is responsible for container management, tracking
+of keyboard and mouse focus and handling external events like resizing of the
+display. The infrastructure layer also decides when to flush the buffer and
+refresh the screen. I.e. The widgets update content of a back buffer and the
+infrastructure decides when it is synchronized to the display.
+
+The **widgets layer** contains the implementations of individual widgets. Each
+widget receives a canvas from the container on which it presents its content to
+the user. Widgets indicate to the infrastructure layer if they support input
+events, which are then forwarded from the infrastructure layer.
+
+The user interacts with the widget API when constructing individual widgets and
+with the container API when placing the widgets onto the dashboard.
+
+![hld](hld.png "High-Level Design")
+
 ## Detailed design
 
+### Display
+
+### Infrastructure
+
+### Widgets
+
+## APIs
+
+### Display API
+
+The Display API is an interface private to the terminal dashboard library. Its
+primary purpose is to act as a shim layer over different display
+implementations.
+
+The API allows to:
+
+- Set values and attributes of cells on a back buffer representing a 2-D
+  canvas.
+- Flush the content of the back buffer to the output.
+- Manipulate the cursor position and visibility.
+- Read input events (keyboard, mouse, display resize, etc...).
+
+The following outlines the display API:
+
+```go
+// Display abstracts an implementation of a 2-D display.
+// A display consists of a number of cells.
+type Display interface {
+  // Size returns the display width and height in cells.
+  Size() image.Point
+
+  // Clear clears the content of the internal back buffer, resetting all cells
+  // to their default content and attributes.
+  Clear() error
+  // Flush flushes the internal back buffer to the display.
+  Flush() error
+
+  // SetCursor sets the position of the cursor.
+  SetCursor(p image.Point)
+  // HideCursos hides the cursor.
+  HideCursor()
+
+  // SetCell sets the value of the specified cell to the provided rune.
+  // Use the options to specify which attributes to modify, if an attribute
+  // option isn't specified, the attribute retains its previous value.
+  SetCell(p image.Point, r rune, opts ...CellOption)
+
+  // Event waits for the next event and returns it.
+  // This call blocks until the next event or cancellation of the context.
+  Event(ctx context.Context) Event
+}
+```
+
+The **Event()** method returns the next input event. Different input event
+types are defined as follows.
+
+```
+// Event represents an input event.
+type Event interface {
+  isEvent()
+}
+
+// Keyboard is the event used when a key is pressed.
+// Implements Event.
+type Keyboard struct {
+  // Key identifies the pressed key.
+  Key rune
+}
+
+func (*Keyboard) isEvent() {}
+
+// DisplayResize is the event used when the display was resized.
+// Implements Event.
+type DisplayResize struct {
+  // Size is the new size of the display.
+  Size image.Point
+}
+
+func (*DisplayResize) isEvent() {}
+
+// Mouse is the event used when the mouse is moved or a mouse button is
+// pressed.
+// Implements Event.
+type Mouse struct {
+  // Position of the mouse on the display.
+  Position() image.Point
+  // Button identifies the pressed button if any.
+  Button MouseButton
+}
+
+func (*Mouse) isEvent() {}
+```
+
+### Container API
+
+### Widget API
+
 ## Project information
 
 ## Caveats
@@ -20,5 +162,20 @@
 
 ## Document history
 
-Date | Author | Description
------|--------|------------
+Date        | Author | Description
+------------|--------|---------------
+24-Mar-2018 | mum4k  | Initial draft.
+
+## Notes (work in progress)
+
+- container styling, borders.
+- coordinates translation for widgets.
+- library to parse events and identify known keyboard shortcuts.
+- widget API (creation, options, updating displayed status, reading inputs).
+- infra API for widgets.
+- widget registration options (subscribe to input / events).
+- testing framework (fake display and test helper functions).
+- container and splits (layout management).
+- buffer sync managed by infra.
+- focus of keyboard and mouse (follow mouse / click).
+- registration for system-wide events (like quit shortcuts).
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