Relative values for line height (percentage, %)
At the moment text leading is made in the same way as in InDesign, its auto or set in px. As we make prototypes for web, text leading could be set the same way as in CSS: in % or just as value: e.g. 1.5. At the moment in XD if you set text leading. for example 13px, all character styles used in text frame have it set to this value.