You're seeing just the function add_unnaccented_search_column, go back to Forage.Search module for more information.
Link to this function

add_unnaccented_search_column(table, column_name, columns)

Adds a new column (named column_name) to the table. The new column will be a concatenation of the columns. The new column will be updated whenever any of the columns changes.

This function is meant to be used in a migration file.

To be able to use this functions you must have already defined the forage_unaccent() PostgreSQL function. The reason why we can't use unaccent directly is quite obscure; you can read more aboute it here