There is almost no documentation about WordPress SHORTINIT constant. It is mainly used when people need to load wp-core minimally (SHORTINIT is being checked in wp-settings.php) as opposed to complete WP Load without it.
We made a dump of complete (for now) list of dump of available functions, classes and constants, when using SHORTINIT:
RESULTS –>https://pastebin.com/3cfmH1C0
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Btw, test was made using:
function get_all() {
return [
'get_declared_classes' => get_declared_classes(),
'get_declared_interfaces'=> get_declared_interfaces(),
'get_declared_traits' => get_declared_traits(),
'get_defined_constants' => get_defined_constants(),
'get_defined_functions' => get_defined_functions(),
'get_defined_vars' => get_defined_vars(),
'get_included_files' => get_included_files()
];
}
$initial_array = get_all();
define('SHORTINIT', true);
require_once( __DIR__ . '/wp-load.php' );
$current_array = get_all();
and WinMerge to compare the results.
RESULTS for initial call (before WP load) –> https://pastebin.com/39A1eQzv