> For the complete documentation index, see [llms.txt](https://www.oulan.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.oulan.com/2017/01/28.md).

# 28

![](/files/-MSkP2BCukc2Y7PrAZNE)