You can include any plain text you want: TXT, HTML, XML, PHP, C, CSV, SQL...
TXT, HTML, and XML will be just printed out into your page like HTML. PHP will be evaluated and run if its contents are placed <?php within PHP marks ?>. It you don't use the PHP marks, plain code will be printed without ever being executed. Any other format will be printed without ever being executed.
Luciano ES
Santos, SP - Brasil