Breaking multiple values in an attribute into multiple lines?

Question

Breaking multiple values in an attribute into multiple lines?

666 Views Asked by its_me At 04 April 2025 at 09:53

Let me explain by example:

<html lang="en-US" prefix="og: http://ogp.me/ns# fb: http://ogp.me/ns/fb# article: http://ogp.me/ns/article#">

    ...

</html>

As you can see, the prefix attribute in the html tag has multiple definitions. How do I break them into multiple lines? (Considering that a line break is equivalent a space when minified back into a single line... it's kinda tough.)

Is this considered normal?

<html lang="en-US" prefix="
    og: http://ogp.me/ns#
    fb: http://ogp.me/ns/fb#
    article: http://ogp.me/ns/article#
">

EDIT: Facebook does it like this: https://developers.facebook.com/docs/payments/product/

<html lang="en-US" prefix=
    "og: http://ogp.me/ns#
    fb: http://ogp.me/ns/fb#
    article: http://ogp.me/ns/article#">

Original Q&A

There are 2 best solutions below

**Lasse** · Answer 1

I don't think it's all that "normal". In general, like the comments to your question suggest, it's technically possible but you're opening your page up to (unnecessary) potential parsing errors.

Look to the HTML WG's example regarding using newlines in the title attribute as a concrete example of this.

Furthermore, I was unable to find/remember a single case where I'd seen this used on purpose, with the exception of SVG (but that's not technically HTML).

However, if you run this sample through the W3C's validator, it'll pass with no errors or warnings in regards to multi-line attributes:

<!DOCTYPE html>
<html lang="en-US" prefix="
    og: http://ogp.me/ns#
    fb: http://ogp.me/ns/fb#
    article: http://ogp.me/ns/article#
">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Hello</title>
</head>
<body>
<h1>Hello World!</h1>
</body>
</html>

Generally, it's better to be safe than sorry. Since I couldn't find any examples to the contrary in this case, I'd venture to say that other developers would agree (Do by all means correct me if I'm wrong).

**Jukka K. Korpela** · Answer 2

The attribute values are different. Each whitespace character is stored in the DOM. Whether the difference matters depends on the definition of the attribute. Many attributes, such as class, are defined as taking a set of whitespace-separated tokens as value, and for them, the amount and type of whitespace characters between tokens, or before the first token and after the last token, does not matter.

The prefix attribute is not present in HTML specifications or drafts. The relevant specification is RDFa Core 1.1, which defines the prefix attribute as “a white space separated list of prefix-name IRI pairs” and contains examples like

<html
  xmlns="http://www.w3.org/1999/xhtml"
  prefix="foaf: http://xmlns.com/foaf/0.1/
          dc: http://purl.org/dc/terms/"
  >

So for the prefix attribute, formatting as in the question is acceptable. (Whether it is “normal” in a sense other than “conforming” is a matter of opinion.)

Breaking multiple values in an attribute into multiple lines?

There are 2 best solutions below

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