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Comment by sorenjan | Hacker News Reader

I sometimes see texts where ä is rendered as a¨, i.e. with the dots next to the a instead of above it even though it's a completely different letter and not a version of a. I managed to track the issue down to MacOS' normalization, but it has happened on big national newspapers' websites and similar. I haven't seen it in a while, maybe Firefox on Windows renders it better or maybe various publishing tools have fixed it. It looks really unprofessional which is a bit strange since I thought Apple prides themselves on their typography.

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I have never see that on all my years on a Mac (though admittedly I’m not dealing in languages where I encounter it often). I’m assuming there’s an issue with the gpos table in the font you’re using so the dots aren’t negative shifted into position as they should be?

Well the point is that ä is one character, not two. It shouldn't be "a with two dots on it", it should be ä. It's its own letter with its own key on Swedish keyboards. MacOS apparently normalizes it to be two characters, and then somewhere in the publishing chain it gets mangled and end up as a¨. I have no doubt that it looked ok on the author's Mac.

It's been a while since I last saw it, but it wasn't because of the font since it was published on a Swedish newspaper's website and other texts worked fine.

A single Unicode codepoint could be represented in a couple of different ways (either decomposed into 2 or as 1). Assume it’s the single codepoint representation.

The font you’re using can (and probably will) rewrite it as 2 glyphs using the GSUB table. This makes sense because it’s a more efficient way to store the drawing operations. The GPOS table is then responsible for handling the offset to put things in their right place.

Main point is that it’s up to the font to move things about.

Now, that may not be what was going on in your case at all but it’s possible.

I have that in gnome terminal. The dots always end up on the letter after, not before. At least makes it easy to spot filenames in decomposed form so I can fix them.

Some old system fonts or old character rasterization engines had problems with certain diacritics, like breve, and they were moved to the space between or after characters. Some Wikipedia articles simply mention that

> Characters may not combine well on some computers.

It was easy to detect people typing or editing text on Apple devices because “their” characters appeared broken, unlike usual single codepoints.

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