In fact, most people believe that to build a RESTful API you can simply create an API based on URLs and HTTP verbs. This is absolutely false. This misunderstanding is going around for too long.

Historically, the uncertainty principle has been confused[5][6] with a related effect in physics, called the observer effect, which notes that measurements of certain systems cannot be made without affecting the system, that is, without changing something in a system.

Just throwing in <div class="{$$props.class || ''} otherChildClass"></div> seems the easiest, and it'll avoid undefined classes. I feel like many aren't noticing the undefined values getting inserted in their classes.

Common misuse example and how to fix it

A common mistake is to see those escaped angle brackets, and "improve" the helper by making everything html_safe: