There will be a strange line under the PHP opening and closing tag as you can see in the screenshot below:
This happens when I write PHP inside an HTML tag like:
<a href="<?php echo '#'; ?>">Hello</a>
so the strange line will be gone if it’s outside the HTML tag like:
<a href="#"><?php echo 'Hello'; ?></a>
This is a PHP file, what is the underline mean? I don’t think the syntax you can see in the screenshot is wrong?