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Concepts
This section of the documentation covers the use of Objects, Libraries and References, Notations, Styles and Types and how each is created, edited and used in the Sym application.
Styles
Each notation refers to a stylesheet. Stylesheets define Styles. Styles are used in two places. First, they can be used to style text. Second, they can be used to style parts of an expression in a rendering. You can create new style and new stylesheets.
Style Functions
Part of the process of generating a rendering expression for any expression is getting and applying the styles for the expression.

Concepts
This section of the documentation covers the use of Objects, Libraries and References, Notations, Styles and Types and how each is created, edited and used in the Sym application.
- Objects
  An object is the basic building block of all of the symbolic content contained in a document - every term in every symbolic expression in Sym is an instance of an object. Many of the objects used in Sym have an object definition that specifies how the object looks and behaves, but it's also possible to create objects that don't have object definitions. All objects are identified by their name and object names are always defined in a specific namespace. All object definitions contain a type definition. Optionally, objects can also contain Properties, Clauses, Renderings, and a Description.
- Library Locations and References
  Locations are used to manage groups of libraries and documents. The purpose of locations is to make documents portable from one machine to another. To do that, locations can be online as well as on your local machine. If a document references online libraries, the required libraries will be downloaded automatically when the document is opened.
- Notations and Rendering
  The purpose of notations is to make it possible to easily change the way expressions are displayed. Notations are assigned to Document Modules, Unit Test Modules and Object Modules. The notation assigned determines which renderings are selected for each expression in the module.
- Styles
  Each notation refers to a stylesheet. Stylesheets define Styles. Styles are used in two places. First, they can be used to style text. Second, they can be used to style parts of an expression in a rendering. You can create new style and new stylesheets.
  - Creating Styles
    Styles are defined in Stylesheets. Stylesheets are functions that return the style settings for a given class name. In this topic, we will cover adding new styles to an existing stylesheet. Creating new stylesheets is covered separately.
  - Creating Stylesheets
    Stylesheets determine the fonts and sizes that are used when objects are displayed. They are designed somewhat like cascading style sheets. Creating a new stylesheet just involves creating a new object definition for the new stylesheet.
  - Style Functions
    Part of the process of generating a rendering expression for any expression is getting and applying the styles for the expression.
- Types
  Every term in every expression in a Sym document has a type assigned to it. Every object definition has a type definition as one of its components. Since type definitions can include things like type variables, Sym uses a type inferencing process to determine the explicit types assigned to each term in every expression.

Style Functions

Part of the process of generating a rendering expression for any expression is getting and applying the styles for the expression.

The BuildRendering function is the heart of the rendering system. It's called each time on expression needs to be rendered on the screen. It takes an expression and the current display settings for the module (which include the edit mode, the notation and the module type) and it returns a rendering expression.

As part of the processing in the BuildRendering function, both the GetStyles and ApplyStyles functions are called. The GetStyles function determines the colors, parenthesizing, and background for each object as it is being rendered. It takes the expression that is going to be rendered and the current display settings for the module and returns a list of zero or more styles that should be applied to the rendering.

The ApplyStyles function applies styles to a rendering expression. It takes a rendering expression and a list of zero or more styles (which typically are provided by the GetStyles function) and returns a rendering expression that includes the style settings provided.

Note that parentheses appear only in the renderings of objects and are not part of the expression. In some cases, we may parenthesize an object differently depending on how it's rendered. For example, when the Div object is rendered horizontally we need parentheses if either the numerator or denominator is, for example, an Add object.

Parentheses are part of the styles for an expression. For example, if the current expression has two parameters and the second parameter should be parenthesized, the styles returned by the GetStyles function will include parentheses: 2 and the ApplyStyles function will use this information to insert parentheses around the second parameter. Note that the parameter of the Parentheses object can be a List of numbers. In this case, more than one parameter will be parenthesized.