A component is represented by an HTML attribute

<a-entity width>

A component’s properties are passed via a string into a HTML attribute where it will be parsed later.

If a component has only one property to define, then it looks like a normal HTML attribute

<a-entity width="1">

If a component has more than one property to define, then properties are passed in through a syntax similar to inline CSS styles

<a-entity geometry="primitive: box; width: 1">

Further reading: