when i use Search.Repositories, set TextMatch = true, but it doesn't work

this is my code:

repos, resp, err = client.Search.Repositories(ctx, query, &github.SearchOptions{
		Sort:      sort,
		Order:     order,
		TextMatch: true,
		ListOptions: github.ListOptions{
			Page:    page,
			PerPage: perPage,
		},
	})

I found it in go-github, in search function, use switch to add Accept to the req.Header, it lead to i can't get text_matches in reponse when i use commits topics repositories issues

I don't know why it's designed in this way, and i didn't found other accept values other than application/vnd.github.v3.text-match+json on the github restful api, such as application/vnd.github.mercy-preview+json . In fact, i don't know what application/vnd.github.mercy-preview+json will do even if i read the documentation