How Do Character Properties Impact Line Height in CSS Rendering?

Can Character Properties Affect Line Height?

In code involving line height and character properties, such as:

<p></p>

we encounter varying behavior across browsers. Firefox may display the text differently, leading to questions about the intended outcome.

Determining the Correct Behavior

The correct behavior for this scenario is not definitively defined, as it depends on several factors:

• Browser Rendering Engine: Each browser has its own rendering engine, which can interpret CSS properties slightly differently.
• Operating System: The operating system can also influence rendering behavior, especially regarding font rendering.

Character Influence on Line Height

Specific characters, like the underscore ("_"), may not strictly alter the line height, but they can determine the line box, along with the line height property. While most character sets do not significantly impact line height, there are exceptions, such as characters with descenders that extend below the baseline.

Line Box vs. Content Area

It's crucial to distinguish between the line box defined by the line-height property and the content area defined by the font characteristics. The line-height property controls the height of the line box, which encompasses all characters, while the font properties determine the height of the individual characters within that box.

Sample Illustration

The following code snippet demonstrates this principle:

span {
  background:red;
  color:#fff;
  font-size:20px;
  font-family:monospace;
}

body {
  margin:10px 0;
  border-top:1px solid;
  border-bottom:1px solid;
  animation:change 2s linear infinite alternate;
}

@keyframes change {
  from {
    line-height:0.2
  }

  to {
    line-height:2
  }
}

<span>
  blah_blah
</span>

As the line height changes dynamically, the content area remains constant while the line box expands and collapses. This illustrates the independent nature of character properties and line height.

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