> For the complete documentation index, see [llms.txt](https://docs.en.avalonia.css.nlnet.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.en.avalonia.css.nlnet.net/documentation/acss-yu-fa/hang-wei.md).

# Behavior

## Behavior Syntax

The [definition of behavior](/documentation/zhu-ti-bang-zhu/ru-he-shi-yong-acss.behaviors.md) has already been mentioned. 

Behaviours are simple to use, similar to Setters, using the name of the behavior set as the attribute and the name of the behavior as the value. 

For example, the behavior `window.esc.close` belongs to the built-in behaviour set acss, and is used in the following way:

```css
Window{
    Background: red;
    .acss:window.esc.close;
}
```

If you customise the behaviour set xbeh, which defines the behaviour window\.xxx.xxx within it, use it as follows:

```
Window{
    Background: red;
    .acss:window.esc.close;
    .xbeh:window.xxx.xxx;
}
```