Single-line comment in HTML

Is there a way to comment out a single line in HTML using just an escape sequence at the start of the line?

Similar to using # or // in other languages? Or is <!-- ... --> the only option for commenting in HTML?

From HTML comments:

>

Since HTML is officially an SGML > application, the comment syntax used > in HTML documents is actually the SGML > comment syntax. Unfortunately this > syntax is a bit unclear at first.

>

The definition of an SGML comment > is basically as follows:

> A comment declaration starts > with <!, followed by > zero or more comments, followed by > >. A comment > starts and ends with > "--", and does not > contain any occurrence of > "--".

This > means that the following are all legal > SGML comments:

1. <!-- > Hello -->
2. <!-- > Hello -- -- Hello--> >
3. <!----> >
4. <!------ Hello > -->
5. <!>

> Note that an "empty" comment tag, with > just "--" characters, > should always have a multiple of four > "-" characters to be > legal. (And yes, > <!> is also a legal > comment - it's the empty comment).

> Not all HTML parsers get this right. > For example, "<!------> > hello-->" is a legal > comment, as you can verify with the > rule above. It is a comment tag with > two comments; the first is empty and > the second one contains "> hello". > If you try it in a browser, you will > find that the text is displayed on > screen.

There are two possible > reasons for this:

1. The > browser sees the ">" character and > thinks the comment ends there.
2. The > browser sees the "-->" > text and thinks the comment ends > there.

There is also the > problem with the "--" > sequence. Some people have a habit of > using things like > "<!-------------->" > as separators in their source. > Unfortunately, in most cases, the > number of "-" characters > is not a multiple of four. This means > that a browser who tries to > get it right will actually get it > wrong here and actually hide > the rest of the document.

For > this reason, use the following simple > rule to compose valid and accepted > comments:

An HTML > comment begins with > "<!--", ends with > "-->" and does not > contain "--" or > ">" anywhere in the > comment.

No, <!-- ... --> is the only comment syntax in HTML.

Let's keep it simple. I loved digitaldreamer's answer, but it might leave the beginners confused. So, I am going to try and simplify it.

The only HTML comment is <!-- -->. It can be used as a single line comment or double; it is really up to the developer.

So, an HTML comment starts with <!-- and ends with -->. It is really that simple. You should not use any other format, to avoid any compatibility issue even if the comment format is legitimate or not.

No, you have to close the comment with -->.

TL;DR: For conforming browsers, yes; but there are no conforming browsers, so no.

According to the HTML 4 specification, <!------> hello--> is a perfectly valid comment. However, I've not found a browser which implements this correctly (i.e. per the specification) due to developers not knowing, nor following, the standards (as digitaldreamer pointed out).

You can find the definition of a comment for HTML4 on W3C's website: 3.2.4 Comments

Another thing that many browsers get wrong is that -- > closes a comment just like -->.