Notes
How to have valid HTML5 and force MSIE to use modern rendering engine
$ sudo -s
# echo 'Header set X-UA-Compatible "IE=edge"' >> /etc/apache2/conf-available/headers.conf
# a2enmod headers
# a2enconf headers
# apache2ctl -k restart
# exit
$ sudo -s
# echo 'Header set X-UA-Compatible "IE=edge"' >> /etc/apache2/conf-available/headers.conf
# a2enmod headers
# a2enconf headers
# apache2ctl -k restart
# exit