relative
A length in relation to some known length.
This type is a combination of a length with a ratio. It results from addition and subtraction of a length and a ratio. Wherever a relative length is expected, you can also use a bare length or ratio.
Example
#rect(width: 100% - 50pt)
#(100% - 50pt).length \
#(100% - 50pt).ratio
A relative length has the following fields:
length: Its length component.ratio: Its ratio component.