How to limit the search scope to the current section?

Question

1C-Bitrix

Hello!
It is necessary to limit the scope of the search to the current section. There is a site where this is implemented . Example
Section_id is passed in the url and I did everything according to the instructions from the Lesson of Practice , but the b_search_content_param table is still empty, even after a complete reindexing.
In general, I ask you to help and explain how the restriction of the search area by the current section is implemented on the example site?