Improve documentation for architecture

- Simplify `README.md` by creating and moving some documentation to
`architecture.md`.
- Add more documentation for state handling between layers.
- Improve some documentation to use clearer language.

docs/application.md

@@ -1,44 +1,45 @@
 # Application
 
-- It's mainly responsible for
-  - creating and event based [application state](#application-state)
-  - [parsing](#parsing) and [compiling](#compiling) [application data](#application-data)
-- Consumed by [presentation layer](./presentation.md)
+Application layer is mainly responsible for:
+
+- creating an event-based and mutable [application state](#application-state),
+- [parsing and compiling](#parsing-and-compiling) the [application data](#application-data).
+
+📖 Refer to [architecture.md | Layered Application](./architecture.md#layered-application) to read more about the layered architecture.
 
 ## Structure
 
-- [`/src/` **`application/`**](./../src/application/): Contains all application related code.
-  - [**`collections/`**](./../src/application/collections/): Holds [collection files](./collection-files.md)
-  - [**`Common/`**](./../src/application/Common/): Contains common functionality that is shared in application layer.
-  - `..`: other classes are categorized using folders-by-feature structure
+Application layer code exists in [`/src/application`](./../src/application/) and includes following structure:
+
+- [**`collections/`**](./../src/application/collections/): Holds [collection files](./collection-files.md).
+- [**`Common/`**](./../src/application/Common/): Contains common functionality in application layer.
+- `...`: rest of the application layer source code organized using folders-by-feature structure.
 
 ## Application state
 
-- [ApplicationContext.ts](./../src/application/Context/ApplicationContext.ts) holds the [CategoryCollectionState](./../src/application/Context/State/CategoryCollectionState.ts) for each OS
-- Uses [state pattern](https://en.wikipedia.org/wiki/State_pattern)
-- Same instance is shared throughout the application to ensure consistent state
-- 📖 See [Application State | Presentation layer](./presentation.md#application-state) to read more about how the state should be managed by the presentation layer.
-- 📖 See [ApplicationContext.ts](./../src/application/Context/ApplicationContext.ts) to start diving into the state code.
+It uses [state pattern](https://en.wikipedia.org/wiki/State_pattern) with context and state objects. [`ApplicationContext.ts`](./../src/application/Context/ApplicationContext.ts) the "Context" of state pattern provides an instance of [`CategoryCollectionState.ts`](./../src/application/Context/State/CategoryCollectionState.ts) (the "State" of the state pattern) for every supported collection.
+
+Presentation layer uses a singleton (same instance of) [`ApplicationContext.ts`](./../src/application/Context/ApplicationContext.ts) throughout the application to ensure consistent state.
+
+📖 Refer to [architecture.md | Application State](./architecture.md#application-state) to get an overview of event handling and [presentation.md | Application State](./presentation.md#application-state) for deeper look into how the presentation layer manages state.
 
 ## Application data
 
-- Compiled to [`Application`](./../src/domain/Application.ts) domain object.
-- The scripts are defined and controlled in different data files per OS
-- Enables [data-driven programming](https://en.wikipedia.org/wiki/Data-driven_programming) and easier contributions
-- Application data is defined in collection files and
-- 📖 See [Application data | Presentation layer](./presentation.md#application-data) to read how the application data is read by the presentation layer.
-- 📖 See [collection files documentation](./collection-files.md) to read more about how the data files are structured/defined and see [collection yaml files](./../src/application/collections/) to directly check the code.
+Application data is collection files using YAML. You can refer to [collection-files.md](./collection-files.md) to read more about the scheme and structure of application data files. You can also check the source code [collection yaml files](./../src/application/collections/) to directly see the application data using that scheme.
 
-## Parsing
+Application layer [parses and compiles](#parsing-and-compiling) application data into [`Application`](./../src/domain/Application.ts)). Once parsed, application layer provides the necessary functionality to presentation layer based on the application data. You can read more about how presentation layer consumes the application data in [presentation.md | Application Data](./presentation.md#application-data).
 
-- Application data is parsed to domain object [`Application.ts`](./../src/domain/Application.ts)
-- Steps
-  1. (Compile time) Load application data from [collection yaml files](./../src/application/collections/) using webpack loader
-  2. (Runtime) Parse and compile application and make it available to presentation layer by [`ApplicationFactory.ts`](./../src/application/ApplicationFactory.ts)
+Application layer enables [data-driven programming](https://en.wikipedia.org/wiki/Data-driven_programming) by leveraging the data to the rest of the source code. It makes it easy for community to contribute on the project by using a declarative language used in collection files.
 
-### Compiling
+### Parsing and compiling
 
-- Parsing the application files includes compiling scripts using [collection file defined functions](./collection-files.md#function)
-- To extend the syntax:
-  1. Add a new parser under [SyntaxParsers](./../src/application/Parser/Script/Compiler/Expressions/SyntaxParsers) where you can look at other parsers to understand more.
-  2. Register your in [CompositeExpressionParser](./../src/application/Parser/Script/Compiler/Expressions/Parser/CompositeExpressionParser.ts)
+Application layer parses the application data to compile the domain object [`Application.ts`](./../src/domain/Application.ts).
+
+A webpack loader loads (or injects) application data ([collection yaml files](./../src/application/collections/)) into the application layer in compile time. Application layer ([`ApplicationFactory.ts`](./../src/application/ApplicationFactory.ts)) parses and compiles this data in runtime.
+
+Application layer compiles templating syntax during parsing to create the end scripts. You can read more about templating syntax in [templating.md](./templating.md) and how application data uses them through functions in [collection-files.md | Function](./collection-files.md#function).
+
+The steps to extend the templating syntax:
+
+1. Add a new parser under [SyntaxParsers](./../src/application/Parser/Script/Compiler/Expressions/SyntaxParsers) where you can look at other parsers to understand more.
+2. Register your in [CompositeExpressionParser](./../src/application/Parser/Script/Compiler/Expressions/Parser/CompositeExpressionParser.ts).