How do variables work in mod ReWrite? Example included

Can anybody explain how this is working?

RewriteRule ^update_my_account/([0-9]+开发者_如何学运维)/([0-9]+)/?$      /index.php?page_id=$1&updated=$2 [L]

What part of the URL is $1 and $2 determined by?

$1 means first group anything matched by first ([0-9]+) in your rewrite regex and $2 is second ([0-9]+).

$1 contains whatever is matched by the first expression inside brackets ([0-9]+), and $2 contains whatever is matched by the second ([0-9]+).