[css-writing-modes] Should a combined white space at the end of a line be removed?

Hi,

I checked the following on Safari/Chrome/Firefox for macOS.
http://jsbin.com/nocidux/edit?html,output
<style>
  #tcy {
    border: solid 1px red;
    text-combine-upright: all;
    -webkit-text-combine: horizontal;
  }
</style>
<div style="writing-mode: vertical-rl">
  <span id="tcy"> </span>
</div>

Safari shows the combined white space at the end of the line, but Chrome
and Firefox don't show it.

Should the combined white space at the end of a line be removed?

It looks like Chrome and Firefox remove the combined white space to follow
CSS 3 Text.
https://drafts.csswg.org/css-text-3/#white-space-phase-2
> A sequence of collapsible spaces at the end of a line (ignoring any
intervening inline box boundaries) is removed.

However, Safari doesn't remove the combined white space because it should
be considered as the Object Replacement Character
https://www.w3.org/TR/css-writing-modes-3/#text-combine-layout
> For other text layout purposes, ... the resulting composition is treated
as a single glyph representing the Object Replacement Character U+FFFC.

I guess that Chrome and Firefox consider White Space Processing as line
breaking and follow:
> For line breaking before and after the composition, it is treated as a
regular inline with its actual contents.

I'm not sure if the removing is line breaking because the removing is done
after line breaking.

Which is correct?

Best regards
Yuki Sekiguchi

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