The run-in Display Value

CSS2 had a display value that folded a heading into the paragraph after it, so a run-in title sat inline at the start of the next block.

In 2026: Dead. No current browser supports run-in, so the heading below renders as its own block line instead of joining the paragraph. CSS Display Level 3 dropped the value, and the engines that once shipped it (old Opera Presto, IE8, an early Blink) no longer do.

Where it came from: CSS2 run-in display, W3C 1998. Worked through in Eric Meyer, CSS: The Definitive Guide. Removed by CSS Display Level 3. MDN ↗

<style>
/* CSS2 run-in: a heading meant to fold into the paragraph after it */
h3.runin { display: run-in; font-weight: bold; margin: 0; }
</style>

<h3 class="runin">Ingredients.</h3>
<p>Flour, water, salt. In 1998 this heading was meant to sit
   inline at the very start of this paragraph, as a run-in title.
   Today it renders as its own block line above, because no
   browser supports run-in.</p>