October CMS : How to parse twig & bracket variables stored in a string or a field ?

octobercms_how-to-parse-twig-and-bracket-variables -from-string-or-field.php

// parsing twig 
$theme = Cms\Classes\Theme::getActiveTheme();
if(($stringContainingTwig = $this['page']['meta_title']) !== null ){
  $page_meta_title = Twig::parse($stringContainingTwig, [
    'varName' => "variable value!",
    'separator' => $theme->title_separator ?: ' _ ' ,
    'title' => $this['page']['title'],
    'business_name' => $theme->business_name,
  ]);
}else{
  $page_meta_title = $this['page']['title'].' - '.$theme->business_name;

}
$this['page_meta_title'] = $page_meta_title;


// parsing bracket 
// ToDo