class_exists throws on missing extends/implements and fatal on missing trait

[kkmuffme]

Affected page

https://www.php.net/manual/en/function.class-exists.php

Issue description

class_exists will throw if a class is autoloaded (= 2nd arg is true = default!), but any extends/implements of that class do not exist and cannot be autoloaded

Steps to reproduce

spl_autoload_register( function ( $class_name ) { 
    if ( $class_name === 'Foo' ) {
        require __DIR__ . '/foo.php';
    }
} );
class_exists( Foo::class );

foo.php

class Foo extends Bar {}

Suggested fix

Mention that it can throw an exception if the any of the classes that class extends/implements fails

Mention that it will result in a fatal E_ERROR if any of the "trait use" of the class do not exist (php/php-src#21106)