Is it correct to use single quotes for HTML attributes?

It's certainly valid to use single quotes (HTML 4.01, section 3.2.2). I haven't noticed such a trend, but perhaps there's some framework that powers web sites you've visited that happens to quote using single quotes.

I find using single quotes is handy when dynamically generating HTML using a programming language that uses double quote string literals.

e.g.

String.Format("<a href='{0}'>{1}</a>", Url, Desc)

When using PHP to generate HTML it can be easier to do something like:

$html = "<img src='$url' />";

than concatenating a string with a variable with a string, as PHP parses variables in double-quoted strings.

Someone may use it in PHP to avoid escaping " if they're using double quoted string to parse variables within it, or to avoid using string concatenation operator.

Example:

echo "<input type='text' value='$data'/>";

instead of

echo "<input type=\"text\" value=\"$data\" />";

or

echo '<input type="text" value="' . $data . '" />';

Nowadays I always stick to using double quotes for HTML and single quotes for Javascript.

It's easier when you want to embed double quotes.

In ASP.NET, it's easier to use single quotes if you're using data-binding expressions in attributes:

<asp:TextBox runat="server" Text='<%# Bind("Name") %>' />

Single quotes are perfectly legal in (X)HTML. Using a backslash to escape them, on the other hand, isn't. <img src='http://widget-site-example.com/ross.jpg' alt='Ross\'s Widget' /> is an image with the alt text "Ross\", and empty s and Widget/Widget' attributes. The correct way of escaping an apostrophe in HTML is '.

What's against single quotes?

You can have single/double quotes all over your html code without any problem, as long as you keep the same quoting style inside a current tags ( many browser won't complain even about this, and validation just want that if you start with a quote, end with the same, inside the same propriety )

Free support to random quoting styles!!! (yay ;D )

Let's settle this argument for good

1. Double quotes are OK
2. Single quotes are OK
3. No quotes are OK, as long as you don't have one of these characters:
   • space (obviously)
   • "<" or ">" (makes sense)
   • equal sign (not sure why but ok)
   • any kind of quote: double, single, backtick (again, makes sense)

Funny how some people, even today, stick to the "double quote only" standard which was never really a standard but a convention. Also, if your language has apostrophes as a natural element (English, anyone?) it's more convenient, but in my opinion, increasing the complexity of PHP string compositions is way too high a price to pay for this.