Whats the difference between & and & in HTML5?

Question

What is the difference between & and &?

Like in the code bellow, are both working in the same way?

<a href="mailto:EMAIL?subject=BLABLABLA&body=http://URL, SHORT DESCRIPTION"></a>
<a href="mailto:EMAIL?subject=BLABLABLA&amp;body=http://URL, SHORT DESCRIPTION"></a>

Solution 1

In HTML5, they are equivalent in that example. Traditionally, in HTML, only & was correct — but as with so many things, web developers blithely ignored this inconvenient rule and wrote bare ampersands everywhere. For their part, browsers just "did the right thing" and interpreted these ampersands as ampersands. HTML5 standardized this behavior, so now & is allowed by itself as long as what goes afterward does not look like an entity reference.

Solution 2

& is the html special character for &, which has a special meaning as the sigial for html special characters. The fact that href="&" works is a convenience granted by most browsers who are nice enough to properly deal with invalid HTML, but it is technically incorrect. You want to use & because the entity will be converted into & in the HTML code.

Consider if you used " instead of &. That would end the href value and make the HTML incorrect, right? You want to use ".

See: http://www.w3.org/html/wg/drafts/html/master/single-page.html#syntax-errors "Errors involving fragile syntax constructs" -- in fact it points out that using & is okay if it's not followed by a named character reference, but there are many of those; ideally you would be escaping attribute input more or less automatically.

Comments

[Explosion Pills]

Can you point to the standardization of this behavior in the spec? I'm looking now...

[Chuck]

@ExplosionPills: It actually does it in kind of backwards way. Whereas traditional HTML specified & only as an entity marker, HTML5 specifically forbids only "ambiguous ampersands." It's in the "HTML Syntax" section of the spec.

[Alohci]

@ExplosionPills -The behaviour (as opposed to what is allowed or forbidden) is here: w3.org/html/wg/drafts/html/master/…

[mamacdon]

"Ambiguous ampersand" is defined here: w3c.github.io/html/syntax.html#ambiguous-ampersand