Is it correct to use single quotes for HTML attributes?

Question

Recently I\'ve been seeing a lot of this:

Answer 1

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.

Answer 2

In PHP, echo takes multiples parameters. So, if one would like to omit the concatenation operator, they could done something like and still use double quotes :

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

Answer 3

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.