Question: Regarding comments inside of an HTML page:

For example:

```
<html>
    <head></head>
    <body>
    <!--
    <p><font size="4">--</font></p>
    -->
    </body>
</html>

```

Using <http://validator.w3.org/check>, I get the following error message. Does it make sense?

> 
> Line 6, Column 21: invalid comment declaration: found character "<" outside comment but inside comment declaration
> 
> 
> `<p><font size="4">--</font></p>`
> 
> 
> Check that you are using a proper syntax for your comments, e.g: . This error may appear if you forget the last "--" to close one comment, and later open another.
> 
> 
>

Answer: 
Yes, it makes sense.

To understand the error message, you have to understand the comment tag. It consists of three key parts, the `<!` that starts the tag, the `--` that starts and ends the comment, and the `>` that ends the tag.

When you put `--` inside the text of a comment, you actually end the comment part. The rest of the text until the end of the tag is invalid, as it's not a comment, and you can only have comments inside the comment tag.

You can also have more than one comment in the tag:

```
<!-- comment -- -- another comment -->

```
No, it does intuitively not make sense to most of the logical thinking humans, but the validator has it really right. The `--` denotes a comment delimiter. Also see [W3 validator bug 5555](http://www.w3.org/Bugs/Public/show_bug.cgi?id=5555):

> 
> yes, really invalid. -- is a comment delimiter in XML.
> 
> 
>