Why do browsers parse "" as ""?

Question

I have a file with following the HTML code:

<p><? comment ?></p>

Curl returns a normal response:

$ curl file:///path/to/the/file.html
<p><? comment ?></p>

But when I parse that response with Firefox 69 or Chrome 77, nothing is shown to me, because the HTML code is as follows:

<html><head></head><body><p><!--? comment ?--></p></body></html>

It looks very strange for me. Why does it happen?

Thanks.

Kaiido · Accepted Answer

That's part of HTML tokenizations rules.

The < character made your browser enter the tag-open-state.

12.2.5.6 Tag open state

Consume the next input character:

U+0021 EXCLAMATION MARK (!)

Switch to the markup declaration open state.

U+002F SOLIDUS (/)

Switch to the end tag open state.

ASCII alpha

Create a new start tag token, set its tag name to the empty string. Reconsume in the tag name state.

U+003F QUESTION MARK (?)

This is an unexpected-question-mark-instead-of-tag-name parse error. Create a comment token whose data is the empty string.

Reconsume in the bogus comment state.

...

So your ? character is handled as a known error, and then the parser switches to the bogus comment state, which will put everything until the next > character inside the comment token.

Why do browsers parse "<? ?>" as ""?

Tags:

html

A''

1 Answers

Kaiido

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