In the comments for print() in the manual:
PHP 4 now allows the use of PRINT <<<EOF, much the same way as PERL's PRINT EOF>>. When using this option there is no need to escape characters such as quotes. This is very useful for printing large amounts of HTML code e.g.
<pre>
print <<<EOF
<pre_tag here>
This is "quoted text"
More quoted stuff "here"
</pre_tag here>
EOF;
</pre>
Make sure not to indent the EOF; statement as this will cause parsing errors.
Basically I think you can use anything in place of EOF or END, so long as they match. Make sense?