I just found this out myself a few days ago. Amazing what is in the manual.
print only takes one argument and displays it.
echo can take multiple arguments separated by commas.
echo 'Hey there ',
a_function_call(),
"Or something $else";
echo '<option>',
$content,
'</option>;
Note that you don't need to use the . operator to get one long string. I have not dug into the code but it seems reasonable that using commas instead of dots will improve performance a bit.