Is there any difference in the behavior of URLs with & versus & in the query parameters?

General Discussions
#1

Is there any difference in the behavior of URLs with & versus & in the query parameters?

#2

To help you understand the difference the ampersand (&) is a special character in HTML that signifies the start of a character reference. When you see & in a URL, it represents the character reference for an ampersand itself (&).

On the other hand, &current; is not a standard character reference and would be considered an error in HTML. Browsers may attempt to correct this error, but it’s not reliable behavior.

If you were to use a valid character reference, such as ™ for the trademark symbol (™), it would appear in the URL instead of the string you intended.

It’s worth noting that in HTML, a semicolon (;) is typically required to end a character reference, although HTML 4 allows it to be omitted in certain cases. However, some browsers, like Internet Explorer, may have issues with this omission.

#3

Another common error occurs when including a URL that contains an ampersand (“&”) in HTML:

This is invalid:


<a href="foo.cgi?chapter=1&section=2&copy=3&lang=en">

Explanation:

This example generates an error for “unknown entity section” because the “&” is assumed to begin an entity reference. Although browsers often recover safely from this kind of error, real problems can occur in some cases.

For instance, many browsers may incorrectly convert &copy=3 to ©=3, which can cause the link to fail. Similarly, since &lt; is the HTML entity for the left-pointing angle bracket (“<”), some browsers might convert &lang=en to 〈=en. Additionally, one old browser might even interpret &sect;, converting &section=2 to §ion=2.

To avoid these problems when validating your website, you should replace ampersands with &amp; when writing a URL in your HTML markup.

Note that replacing “&” with &amp; is only necessary when writing the URL in HTML, where “&” is a special character (along with “<” and “>”). When writing the same URL in a plain text email message or in the location bar of your browser, you should use “&” and not &amp;. HTML interprets &amp; as “&”, so the web server only sees “&” and not &amp; in the query string of the request.

#4

Here’s a fascinating example: when &current is parsed into a text node, it is converted to ¤t. However, when parsed into an attribute value, it is interpreted as &current.

If you want &current to appear as text in your document, you should write &amp;current in your markup.

For a detailed explanation, you can refer to the HTML5 parsing specification under the “Named Character Reference State” section.