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.my-element { margin-inline-start: 1em; }What this now does is instead of saying “add margin to the left”, it says “regardless of direction, put margin on the starting side”. If the language of the document was right to left, like Arabic, that margin would be on the right hand side.
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This is clever. If you use e.g. margin-left on every list element after the first to put space “between” them, the spacing isn’t quite right when the order of the elements
is reversed, for example because your page has been automatically translated into a language that reads in the opposite direction (e.g. right-to-left, rather than left-to-right). When
you use margin-left in this way you’re imposing a language-direction-centric bias on your content, and there’s no need: margin-inline-start and its friends
are widely-supported and says what you mean: “place a margin before this element”. I’ll be trying to remember to
use this where it’s appropriate from now on.