A set of name-value pairs. The name should be a valid vega
property.
The first two unnamed components are taken to be x and y.
Any additional unnamed components will raise an error.
.props
When calling props from other functions, you'll
often have a list of quoted function functions. You can pass that function
to the .props argument instead of messing around with
substitute. In other words, .props lets you opt out of the
non-standard evaluation that props does.
inherit
If TRUE, the defaults, will inherit from properties
from the parent layer If FALSE, it will start from nothing.
env
The environment in which to evaluate variable properties.