There are two series of interfaces that make Freon and its generated code extensible and flexible.
The first series are the interfaces of the generated code.

The second series of interfaces define the editor framework itself.

The projection from your model or AST is defined by implementing the FreProjection interface.

/* File: core/src/editor/projections/FreProjection.ts  */

/**
 * Interface for a custom projection.
 */
export interface FreProjection {
	// todo add priority

	// Name of the custom projection
	name: string;

	// The projection handler that this projection is registered in.
	handler: FreProjectionHandler;

	// A map from the name of the concept (or the freLanguageConcept() of the FreElement node) to
	// the function that may return the custom box for a node of that type.
	nodeTypeToBoxMethod: Map<string, (node: FreNode) => Box>;

	// A map from the name of the concept (or the freLanguageConcept() of the FreElement node) to
	// the function that may return the custom box for a node of that type.
	nodeTypeToTableDefinition: Map<string, () => FreTableDefinition>; // todo change name and remove Tabledefinition type
}

Implementing this interface should return a Box for each element in the AST.
Freon includes many predefined boxes (textual, tabular, horizontal or vertical collections, etc.)
to define this projection.

The box model is further described in the Editor Framework documentation.

An object that implements FreExpressionNode represents a typed node within the model AST that behaves as an expression.

/* File: core/src/language/FreExpression.ts */

export interface FreExpressionNode extends FreNode {}

An object that implements FreBinaryExpression is a node in the model AST.
It represents an expression that has exactly two operands, which are usually written to the left and right of the operator symbol (for example, 4 + 5).

This interface extends FreExpression.

/* File: core/src/language/FreBinaryExpression.ts */

export interface FreBinaryExpression extends FreExpressionNode {
	freLeft(): FreExpressionNode;

	freSetLeft(left: FreExpressionNode): void;

	freRight(): FreExpressionNode;

	freSetRight(right: FreExpressionNode): void;

	frePriority(): number;
}

In both series of interfaces, the following two core interfaces are reused:

• FreNode
• FreNamedNode