Rectangle

Property	Type	Description
`type`	`'rect'`
`condition`	`formula` (optional)
`repeat`	repeat (optional)
`step`	`boolean, formula` (optional)
`defs`	Definition[] (optional)
`x`	`number, formula` (optional)	The x-coordinate of this rectangle, relative to its bounds (default: 0)
`y`	`number, formula` (optional)	The y-coordinate of this rectangle, relative to its bounds (default: 0)
`w`	`number, formula` (optional)	The width of this rectangle, relative to its bounds (default: 1)
`h`	`number, formula` (optional)	The height of this rectangle, relative to its bounds (default: 1)

{
  type: "rect"
  // NOTE: Unspecified x and y default to 0.
  // NOTE: Unspecified w and h default to 1.
}

{
  type: "rect",
  x: 0.5,
  y: 0.5,
  w: 0.5,
  h: 0.5
}