To provide more flexibility in handling quotes, allow the backtick quote
  for SSI tag arguments (e.g. <!--#echo val=`foo` -->).  This helps with
  arguments containing both single and double quotes.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92678 13f79535-47bb-0310-9956-ffa450edef68