Are single quotes allowed in HTML?

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?

Solution 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.

Solution 2:

As noted by PhiLho, although there is a widely spread belief that single quotes are not allowed for attribute values, that belief is wrong.

The XML standard permits both single and double quotes around attribute values.

The XHTML standard doesn't say anything to change this, but a related section which states that attribute values must be quoted uses double quotes in the example, which has probably lead to this confusion. This example is merely pointing out that attribute values in XHTML must meet the minimum standard for attribute values in XML, which means they must be quoted (as opposed to plain HTML which doesn't care), but does not restrict you to either single or double quotes.

Of course, it's always possible that you'll encounter a parser which isn't standards-compliant, but when that happens all bets are off anyway. So it's best to just stick to what the specification says. That's why we have specifications, after all.

Solution 3:

I have heard people saying that single quotes for HTML fields is not recognized by EVERY browser

That person is wrong.

Solution 4:

Don't believe everything you see on Internet...
Funnily, I just answered something similar to somebody declaring single quotes are not valid in XHTML...

Mmm, I look above while typing, and see that Adam N propagates the same belief. If he can back up his affirmation, I retract what I wrote... AFAIK, XML is agnostic and accepts both kinds of quote. I even tried and validated without problem an XHTML page with only single quotes.

Solution 5:

Only problem is data going into TEXT INPUT fields. Consider

<input value='it's gonna break'/>

Same with:

<input value="i say - "this is gonna be trouble" "/>

You can't escape that, you have to use htmlspecialchars.