If It Can Be Done Using an HTTP Header, Use an HTTP Header

Post from January 13, 2020 (↻ August 6, 2021), filed under (feed).

The following is a (slightly modified) chapter from Upgrade Your HTML, which is “all about picking examples of HTML in the wild, and explaining how to make that code better.” You can get an inexpensive copy at Leanpub as well as at Amazon.

There are a number of things you can control in HTML that can also be controlled on the domain or protocol level. For example, aspects related to security, performance, or, as in this chapter’s case, redirects (meta elements are infamous when it comes to redirects), even verification and indexing. Whenever that’s the case, you’re better off working with said domain or protocol level.

The reason? Maintainability, for centralization through domain or HTTP configuration makes it a lot easier, faster, and reliable to manage changes.

<meta http-equiv="Last-Modified" content="Monday, 07 October, 2019 02:21:47AM">
<meta name="Last-Modified" content="Monday, 07 October, 2019 02:21:47AM">
<meta name="Last-Modified-Date" content="Mon, Oct 07, 2019">
<meta name="Last-Modified-Time" content="02.21AM IST">

In the case of the markup above, for example, most servers already respond to a request with a Last-Modified header. (The other two headers seem non-standard, but can be provided, too, if necessary.) The server the example site is on is no exception:

Last-Modified: Mon, 07 Oct 2019 21:21:47 GMT

While the sample code gives room for speculation—what was the motivation to add all this meta markup? why not in the standard Last-Modified format?—, the lesson is to use HTTP headers if HTTP headers can be used. Because the best HTML is sometimes no HTML, as with the optimized minimal example code:


An Anecdote

The cover of “Upgrade Your HTML.”

It’s theoretically possible—my last test dates back a while, and only Firefox just passed it again—to also assign style sheets through HTTP headers. The way it works is described in the old HTML 4.01 spec:

Web server managers may find it convenient to configure a server so that a style sheet will be applied to a group of pages. The HTTP Link header has the same effect as a LINK element with the same attributes and values. Multiple Link headers correspond to multiple LINK elements occurring in the same order.

This allows to issue a header like

Link: <https://example.com/default.css>; REL=stylesheet

to be equivalent to:

<link rel=stylesheet href=https://example.com/default.css>

This is the simplest way and the least work to create a style sheet reference—theoretically the only reference for an entire project. If this worked everywhere you had my full recommendation to always and only set your default style sheet like this!

Needless to say, there may be exceptions to the rule, the most obvious one being the case when HTTP headers can’t be set. For a softer version of the rule, replace “use” with “prefer.”

More? Upgrade Your HTML. (If you’re interested in web development and HTML and CSS quality overall, consider the book bundle that also includes CSS Optimization Basics and The Web Development Glossary.)

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About Me

Jens Oliver Meiert, on September 30, 2021.

I’m Jens, and I’m an engineering lead and author. I’ve worked as a technical lead for Google, I’m close to W3C and WHATWG, and I write and review books for O’Reilly. I love trying things, sometimes including philosophy, art, and adventure. Here on meiert.com I share some of my views and experiences.

If you have a question or suggestion about what I write, please leave a comment (if available) or a message. Thank you!