Problem with parser

Try this:

PHP Code:

// ADDED quotes because variables not available
$data = [
  'site_name'      => '$ConfigurationSite->name',
  'seo_title'      => '$ConfigurationSite->title',
  'seo_book_title' => '$SeoBooks->title'
]; 

// http://php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc

// BEWARE OF TRAILING SPACES
$tmp = <<< ____TMP
<meta property="og:description" content="{$data['seo_book_title']}" />

____TMP;
// BEWARE OF TRAILING SPACES

echo htmlspecialchars($tmp); 


Result: 

<meta property="og:description" content="$SeoBooks->title" />