what is a non-replaced inline element?

Encountered the following while reading the height property of CSS2 specification:

>Applies to: all elements but non-replaced inline elements, table columns, and column groups

I understand what replaced element(<img>) or inline element(<button>, <a>) are, but having trouble finding out examples of non-replaced inline elements.

For most practical purposes, it is best to read “replaced” as “embedding”. So “non-replaced element” is just an element that is rendered as such, instead of causing some external content to appear in its place.

The expression “non-replaced inline element” has no definition of its own: it simply refers to any element that is both a non−replaced element and an inline element. Such as <a>. Most elements in HTML are non-replaced. A non-replaced element is simply an element that is not a replaced element.

However, in CSS specifications, there are just general characterizations the concept “replaced element”, not any definitive list of such elements. This is understandable, since HTML evolves rather independently of CSS.

The concept has somewhat changed over time. The CSS 1 spec said: “In HTML, IMG, INPUT, TEXTAREA, SELECT, and OBJECT elements can be examples of replaced elements.” In newer specs, form fields are not included any more. This is reflected in the HTML5 draft, where the Rendering section explicitly lists form controls under Non-replaced elements. The only replaced elements, according to it, are those that embed external content, such as an image, video, applet, or HTML5 canvas into an HTML document – except that the revamped menu element is mentioned too (it is expected to be implement in a manner that echoes browser controls, so it sort-of embeds external content too).

This change reflects browser development. Early browsers implemented form fields using system routines in a manner that was immune to anything in CSS, and there are still some remains of such approaches, but nowadays form fields can mostly be formatted with CSS, so they have effectively changed from replaced to non-replaced elements.

David Baron discusses this on his website here.

> There are two types of inline elements: replaced inline elements and > non-replaced inline elements. In general, non-replaced elements are > those whose content is contained in the document, whereas > replaced-elements are those whose content is outside of the document. > For example, in the code: > > Visit the <a href="http://www.w3.org/">World Wide Web Consortium</a> > to learn about... the content of the a element is "World Wide Web > Consortium". Replaced elements are those where the content comes from > some external source, for example, an object or img element. > > However, as far as the inline box model is concerned, the definitions > are as described above except that elements with display types > inline-table and inline-block (the latter is a proposed type for CSS3 > to accommodate form elements) are considered replaced elements.

Good examples of non-replaced inline elements are span, strong, i, b, em, etc.

You can find the definition of a replaced element in the index:

> An element whose content is outside the scope of the CSS formatting > model, such as an image, embedded document, or applet. For example, > the content of the HTML IMG element is often replaced by the image > that its "src" attribute designates. Replaced elements often have > intrinsic dimensions: an intrinsic width, an intrinsic height, and an > intrinsic ratio. For example, a bitmap image has an intrinsic width > and an intrinsic height specified in absolute units (from which the > intrinsic ratio can obviously be determined). On the other hand, other > documents may not have any intrinsic dimensions (for example, a blank > HTML document). > > User agents may consider a replaced element to not have any intrinsic > dimensions if it is believed that those dimensions could leak > sensitive information to a third party. For example, if an HTML > document changed intrinsic size depending on the user's bank balance, > then the UA might want to act as if that resource had no intrinsic > dimensions. > > The content of replaced elements is not considered in the CSS > rendering model.

A non-replaced inline element is something that is inline and does not conform to the above. Roughly speaking, it is an element containing (or that can contain) text that can be styled normally. (a, b, cite, def, em, etc)