Does a Single Character Affect Line Height in Different Browsers?

Can Line Height be Affected by Specific Character

This article investigates whether a specific text character can alter the line height in rendering, a behavior noticed in Firefox for Windows 10.

The provided code snippet shows two paragraphs with an ASCII underscore character added in one instance. In Firefox, the underscore causes the line height to decrease and cuts the character, while other browsers do not exhibit this behavior.

The question arises as to which behavior is correct. line-height: 1 typically implies the ability to fit any text into a line of that size. However, character design can introduce specific challenges.

Correct Behavior

All observed behaviors are considered correct due to the variation in default fonts across browsers and operating systems.

Line Height and Character Design

Line-height affects the line box size, but it does not directly control character rendering. Characters are defined by the font's content area, which is not influenced by line-height.

Line-height: 1 does not guarantee that any character will fit within the specified height, as the font may not have designed its characters to fit within that space.

Example

The following code snippet demonstrates the distinction between the line box and content area. As the line height changes, the red background of the span element (representing the line box) varies in size, while the text (representing the content area) remains unchanged:

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