# Type System Reference

The typesystem is used by a binding generator or any other software using the APIExtractor library to map a C++ library API onto a higher level language.

The typesystem specification is a handwritten XML document listing the types that will be available in the generated target language API; types that are not declared in the specification will be ignored along with everything depending on them. In addition, it is possible to manipulate and modify types and functions. It is even possible to use the typesystem specification to inject arbitrary code into the source files, such as an extra member function.

Below there is a complete reference guide to the various nodes (XML tags) of the typesystem. For usage examples, take a look at the typesystem files used to generate PySide2. These files can be found in the PySide2/<QT_MODULE_NAME> directory of the PySide2 package.

## Define types

- Specifying Types

## Code generation

- Code Generation Terminology

## Modifying types

- Modifying Arguments
- Code Injection Semantics
- User Defined Type Conversion
- Using Code Templates
- Modifying Functions
- Manipulating Object and Value Types
- Conversion Rule Tag
- Manipulating Documentation
- Type System Variables

## Object ownership

- Object ownership

## Extra options and Python caveats

- Solving compilation problems
- Sequence Protocol