gistfile1.txt

# Properties
The properties are implemented in the [ui/core/properties/properties.ts](https://github.com/NativeScript/NativeScript/blob/master/tns-core-modules/ui/core/properties/properties.ts).
A little bit like XAML properties, these objects define properties on the View, ViewBase or Style classes.
 - Property
 - InheritedProperty
 - CssProperty
 - CssAnimationProperty
 - ShorthandProperty

The property classes unify the way:
 - object.defineProperty is made
 - handle change notifications
 - handle native getter/setter
 - handle css value convertion
 
 - nativeValueChange - get notified by native controlls that a native value had change and we have to update the JavaScript value

# CSS
## CSS3 Parser
The spec: https://www.w3.org/TR/css-syntax-3/
The currently used CSS parser is ["rework"](https://github.com/NativeScript/NativeScript/tree/master/tns-core-modules/css), may be changed in future.
The parser is used to convert CSS strings to rules with selectro strings and key-value objects for the CSS declarations.

## CSS Selectors Parser
The spec: https://www.w3.org/TR/selectors4/
The selectors strings provided by the CSS3 parser are converted to AST:
https://github.com/NativeScript/NativeScript/blob/master/tns-core-modules/ui/styling/css-selector-parser.ts
The parser is inhouse grown selectors parser close to the spec.
May move and be merged with a css parser to consume the input tokens produced by the CSS parser.

And the AST to object model that is capable of performing matches on View-like objects:
https://github.com/NativeScript/NativeScript/blob/master/tests/app/ui/styling/css-selector.ts

## Applying CSS
Css on views is applied by some code integrated in the View classes and the style-scope:
https://github.com/NativeScript/NativeScript/blob/master/tns-core-modules/ui/styling/style-scope.ts

Selectors are split in two groups:
 - Dynamic: depend on attributes, pseudo-classes etc. listen for events
 - Static: depend only on the visual tree, id and className attributes

The CssState class is responsible to listen for changes that will invalidate the dynamic state
and apply CSS properties on the View instances