enhancement: Provide a way to use a group of attributes in rect

[stevenxxiu]

I often use the same attributes in rect. It'll be good if there was a way to use a group of them at once, to reduce code duplication.

As an example, suppose I often use direction: "vertical", spacing: 10. I want to be able to write something like custom_rect { color: "green", width: 100% }, or rect { custom_attributes, color: "green", width: 100% }.