Are single quotes allowed in HTML?

Question

I am a big time user of using double quotes in PHP so that I can interpolate variables rather than concatenating strings. As a result, when I am generating HTML I often use single quotes for setting tag fields. For example:

$html = "<input type='text' name='address' value='$address'>";

Now this is far more readable to me than either

$html = "<input type="text" name="address" value="$address">";

or

$html = '<input type="text" name="address" values="' . $address . '">' ;

From brief searches I have heard people saying that single quotes for HTML fields is not recognized by EVERY browser. Thus I am wondering what browsers would have problems recognizing single quote HTML?

Answer 1

This is similar to When did single quotes in HTML become so popular?. Single quotes around attributes in HTML are and always have been permitted by the specification. I don't think any browsers wouldn't understand them.