Is there a way to comment multiple lines... which already have some comments in them?
i.e.
<html>
<!-- Multi-line comment begin
<head>
<!-- This script does abcxyz -->
<script>...</script>
</head>
<body>
Hello world!
</body>
Multi-line comment end -->
</html>
It seems that even SO's syntax hilighting won't accept this...
No. Comments cannot be nested and HTML has only one style of comment.
I think the key point is this:
Note that comments are markup.
http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.2.4
This is not valid markup:
<div <span/> />
... so neither is the one you mention.
Since all my sites are written in PHP I normally comment out code with PHP comments:
<?/*?>
<div>...</div>
<p>...</p>
<?*/?>
Perhaps you can use a similar trick.
No. The closing comment tag --> will always end the comment section so if your comment includes a comment the closing tag of your included comment will end the comment section.
You can do a replace of --> in the section you are about to comment out to something unique so you can later just do another replace back to --> if you choose to undo your commenting.