Is the default value of FORCE_SSL_ADMIN documented?

I got stuck for a while trying to understand how comes the site I’m managing performs HTTP to HTTPS redirection since:

  • I enabled SSL connection
  • I didn’t put a .htaccessfile
  • I didn’t set the FORCE_SSL_ADMIN constant in wp-config.php

Once I figured out the redirection was performed by WordPress and not the HTTP server, I ended up triying to do a massive grep -r 'FORCE_SSL_ADMIN' ./www, and I found this on default-constant.php (WordPress 5.7.2, line 328):

function wp_ssl_constants() {     /**      * @since 2.6.0      */     if ( ! defined( 'FORCE_SSL_ADMIN' ) ) {         if ( 'https' === parse_url( get_option( 'siteurl' ), PHP_URL_SCHEME ) ) {             define( 'FORCE_SSL_ADMIN', true );         } else {             define( 'FORCE_SSL_ADMIN', false );         }     }     /* [...] */ 

If I understand correctly, if the constant isn’t set and the siteurl entry (apparently the URL site value set in Setting page of the dashboard) begins is of scheme HTTPS://, then FORCE_SSL_ADMIN is set to true.

I may have wrongly searched, but what I found led me to think siteurl has to be set in order to let the redirection works, which is not the case.

Is this default behavior (redirection according to the site URL scheme) explained somewhere in the official documentation?