Can comments appear before the DOCTYPE declaration?

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I would like to place a comment ( style) at the very top of my HTML code, preceding the DOCTYPE declaration. Does this conform to the standar

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夕颜

2020-11-27 16:27

Writing the <!DOCTYPE> first is certainly best practice.

I remember strange problems a long, long time ago where some browser (probably IE6) ignored a <!DOCTYPE> because there was something seemingly innocent before it - I think just whitespace, but maybe it was a comment. In any case, it was a horrible, horrible bug to have to track down, and there's certainly never any good reason to have comments or whitespace before the <!DOCTYPE>.

Writing the <!DOCTYPE> first is, I'd say, just something experienced web developers do to avoid horrible, elusive bugs.

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萌比男神i

2020-11-27 16:27

While it's acceptable per the standard I believe, you definately want to avoid it, as it'll throw IE into quirks mode.

(See Triggering different rendering modes)

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北荒

2020-11-27 16:29

Comments before the doctype are allowed, but cause all IE versions to revert to quirks mode. They are, actually, used for that purpose sometimes. The XML declaration (<?xml version ...?>) have the same effect, in IE6 and below.

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感情败类

2020-11-27 16:37
It is fully valid to do
```

<!DOCTYPE html>
```
However, it brings all versions of IE into quirks-mode (unless it is forced into no-quirks mode — see the Gotchas section below). The simplest is to move the comment below the DOCTYPE.
```
<!DOCTYPE html>

```
But another way is to “upgrade” the comment into a suitable conditional comment, such as this:
```

<!DOCTYPE html>
```
Explanation: a conditional comment does not count as a comment, in IE's world.

Alternative syntax: To forget/remember that conditional comments are a Microsoft intrusion into the HTML standard, one could for instance do
```

<!DOCTYPE html>
```
Likewise, to target IE in particular, one could do
```

<!DOCTYPE html>
```
Gotchas

A comment inside a conditional comment will bring IE into quirks-mode if IE sees it (that is: if one uses an [if IE] condition, or an equivalent to [if IE] — such as the [if !anybrowser] condition that I mentioned above.). So, for example, this would bring IE in quirks-mode:
```
<![if IE]><![endif]>
<!DOCTYPE html>
```
As would
```

<!DOCTYPE html>
```
and many other variants. Whereas for example
```

<!DOCTYPE html>
```
would not cause quirks-mode, because here the conditional comment has a DOCTYPE before any other content, and thus IE considers that the first content of the page is a DOCTYPE.

Finally, the newest IE versions, IE8 and IE9, can be forced to standards-mode (and to quirks-mode as well) by the use of another Microsoft invention — the x-ua-compatible directive. See http://msdn.microsoft.com/en-us/library/cc288325(v=vs.85).aspx In that case, then
```

<!DOCTYPE html>

```
will force IE8 and IE9 into no-quirks mode, while IE6 and IE7 will remain in quirks mode. Whereas, in contrast, this
```

<!DOCTYPE html>
```
would force IE8 and IE9 into standards mode, despite that the content of the conditional comment does not start with a DOCTYPE. And IE6 and IE7 will also remain in no-quirks mode since the conditional comment doesn't target them.
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夕颜

2020-11-27 16:41

That may cause IE7 to render in quirks mode as if a doctype was not there at all, according to this page.

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