To provide unified navigation for all parts of kotlinlang.org, the Kotlin Website Team uses this directory to place custom templates in this folder during the website build time on TeamCity.
It is not practical to place these templates in the kotlinx.serialization repository because they change from time to time and aren't related to the library's release cycle.
The folder is defined as a source for custom templates by the templatesDir property through Dokka's plugin configuration.
Here, you can find more about the customization of Dokka's HTML output.