Safari displays spacing between words differently when writing-mode is set to a vertical value, for example vertical-lr, and text-orientation is set to upright. Depending on the font and the ones I tested, it looks like there is no space at all. I couldn't find anything helpful about this on the web and I am not familiar with font rendering. All I can say is that the spacing looks "correct" in the other major browsers. Here is a CodePen with a minimal setup where the issue can be seen and tested: https://codepen.io/glmvc/pen/YzRPoaX Checked in Safari Version 16.5.2 and Safari Technology Preview Release 176 on macOS Ventura 13.4; and in Safari on iOS Version 16.6.
I am able to reproduce this bug in Safari Technology Preview 176 and WebKit ToT (266845@main) where the 'red' one is not matching Chrome Canary 117 and Firefox Nighty 118. Adding 'BrowserCompat' tag.
Adding @Tim - he is doing writing mode these days and @Alan - since he fixed negative letter spacing issue recently. It might not be directly related to them but good to add them or get their inputs (if any).
Safari produces the same result when font is set to Ahem (or Monospace) which makes me think this is more about fonts than layout. Myles? <style> div { writing-mode: vertical-lr; text-orientation: upright; font-family: Ahem; } </style> <div>yes spacing</div>
<rdar://problem/114140150>
Created attachment 467349 [details] rendering in Safari, firefox, chrome The three browsers renders slightly differently indeed. from shortest length to longest safari, firefox and chrome.
Previously Bug 86071 Bug 93304
Created attachment 467350 [details] space size when selected in safari, firefox, chrome. We better the difference in the space sizes across the browsers.
Created attachment 467374 [details] rendering in Epiphany on Linux