Paragraph spacing measurment

You're right.

A Shift Return historically distinguishes from a normal Return, by applying just a carriage return (with its line height), not ending the paragraph yet (without any extra paragraph spacing). This worked since ancient typesetting, in word-processing software back in the early eighties like MacWrite, MS Word, and WriteNow versions 1, and in the first incarnations of HTML and later on CSS by the use of Paragraph and Break tags.

And in Adobe XD ? Nope. Return and Shift-Return are all the same, ending the paragraph.

I wonder if XD will ever dare to implement this difference in text treatment and typographical refinement.

Maybe not, because the rationale might be: let's keep things simple – not production inclined.

By the way, since you're coming from an InDesign background, below some extra points of attention:

First off, the default paragraph incremental height (Return) in InDesign will initially and automatically be just as large as the line height, which is the font size plus 20%. (This Auto percentage is oddly hidden under the Hyphenation setting for a paragraph.) So a 20 pt/px text size will get a 24 pt/px line height, and zero paragraph spacing before and after. So the line height and paragraph spacing will not be equal to the font size. When you start a text line or frame in Adobe XD, the line height will initially behave in the same manner: font size + 20% (though rounded the next integral). Once edited, you can set the line height back to any automatic value by typing in a percentage.

Secondly: in bare bones HTML and CSS, any paragraph always gets some spacing (depending on the browser's default), even when none is set ! So that's why many front-end developers use a so-called "boiler-plate" CSS to set several typography defaults to zero, so any value they state after that will become the prominent one.

Next up: in software like InDesign, paragraph spacing is measured in space before and after. Although similar settings are available in CSS, Adobe XD only offers space after. Maybe because that's all they could think of, maybe because they're afraid to open a can of worms with space before and after. There's this difference you know between old-school print media and modern times web typography. In CSS a combination of after and before spacing will collapse to the largest value. In print media (and in InDesign as well), a combination will be the total of space after and before.

And Finally: don't forget, in InDesign, the Enter key (on the numerical pad, or fn-Return on a standard keyboard) will jump to the next column. And there's obviously no need for anything similar in Adobe XD...

I checked with the team, and they tell me that the units are in points. the same as for all the other measures in Adobe XD.