wp_namespace_example.php

<?php

// this sample is in MU-plugins.  It's just a sample
// pattern about how you can use a namespaced class to 
// decrease how much is injected into the global name space

namespace Materiell;

class Google_AMP_Mods {

    public function __construct() {
        add_filter('amp_post_template_metadata', [$this, 'filter_meta'], 100, 2);
    }

    // make sure that the schema metadata is correct
    public function filter_meta ($metadata, $post) {
        if (
            isset($metadata['author'])
            && isset($metadata['publisher'])
        ) {
            $metadata['author'] =  $metadata['publisher'];
            if (!isset($metadata['publisher']['logo'])) {
                $metadata['publisher']['logo'] = [
                    'type' => 'ImageObject',
                    'url' => 'https://draxe.com/wp-content/themes/draxe2014/images/draxe-logo.png',
                    'width' => '167',
                    'height' => '119',
                ];
            }
        }
        return $metadata;
    }
}

$mat_google_AMP_mods = new Google_AMP_Mods();