What means the PHP warning "Cannot add header information - headers already sent ..."?

HAWHAW automatically creates the correct mime-type in the HTTP response header according to the detected browser. The HTTP header has to be created before any other content is sent. When your application initiates some output, PHP will create a standard header with a mime-type text/html by default. When then HAWHAW tries to create the appropriate header command, it's too late: Header and output are already sent out, there's no way to modify the header afterwards. HAWHAW applications should never use commands like echo or printf because all required output is done by HAWHAW when you call the HAW_deck's object function create_page(). Make sure that there are not empty lines in your script outside of your PHP tags. One single blank character or carriage return before <?php can be enough to create the wrong HTTP header.  more

HAWHAW automatically creates the correct mime-type in the HTTP response header according to the detected browser. The HTTP header has to be created before any other content is sent. When your application initiates some output, PHP will create a standard header with a mime-type text/html by default. When then HAWHAW tries to create the appropriate header command, it's too late: Header and output are already sent out, there's no way to modify the header afterwards. HAWHAW applications should never use commands like echo or printf because all required output is done by HAWHAW when you call the HAW_deck's object function create_page(). Make sure that there are not empty lines in your script outside of your PHP tags. One single blank character or carriage return before <?php can be enough to create the wrong HTTP header.  more