What exactly does the 's' parameter search for in WP queries?

Question

I have a simple question, but can't find the answer anywhere. What exactly does the 's' parameter search when used in a query? Ex:

$args = array( 's' => $keyword ); $query = new WP_Query($args);

Does it just search post content, or does it also look at title, tags, etc?

EDIT: Just to clarify. The question is what post fields are being searched, not what data is being returned.

Answer 1

As usual it's most reliable to dump the resulting SQL query and see:

SELECT wp_posts.ID
FROM wp_posts
WHERE 1=1
  AND (((wp_posts.post_title LIKE '%keyword%')
        OR (wp_posts.post_content LIKE '%keyword%')))
  AND wp_posts.post_type = 'post'
  AND ((wp_posts.post_status = 'publish'))
ORDER BY wp_posts.post_date DESC LIMIT 0,5

The only two things native search is considering are title and content.