ui/richtext/RichTextCommon.cs

A RichText tag handler class for the UI system that matches the word "common" (case-insensitive and allowing optional plural). It sets default styling for that tag: light gray color, italic font, and a font weight of 500.

Reflection
using Sandbox.UI;

[RichTextPanel( @"\b[Cc]ommon?\b" )]
public class RichTextCommon : RichTextBase
{
	public override Color Color => new Color( 0.9f, 0.9f, 0.9f );
	public override bool Italic => true;
	public override int? FontWeight => 500;
}