Set `ry` attribute of the subelement relatively to the height of the element referenced to by the selector in `ref` attribute. If the value is in the `[0, 1]` interval (or expressed in percentages, e.g. `'80%'`), the `ry` of the subelement will be set as a percentage of the height of the referenced element. If the value is `<0` or `>1`, the height of the subelement will be smaller/bigger than the height of the referenced element by the amount specified. Note that this makes sense only for SVG elements that support `rx` and `ry` attributes, such as `<ellipse>`.