None of the strings beginning with c:
are valid URLs, so you can't use them in href
or src
attributes in HTML. You can use them in PHP include
lines because those are processed by the server, and it allows the argument to be local filenames.
<?php include '$menu1' ?>
doesn't work because PHP only expands variables inside doublequoted strings, not inside singlequoted strings. It's just like the difference between:
echo "$menu1";
and
echo '$menu1';
The first will echo the value of the variable, the second will echo $menu1
literally.