A single TextRun for the box tree. These are all descendants of
super::InlineBox or the root of the super::InlineFormattingContext. During
box tree construction, text is split into TextRuns based on their font, script,
etc. When these are created text is already shaped.
Whether or not this character should be able to change the font during segmentation. Certain
character are not rendered at all, so it doesn’t matter what font we use to render them. They
should just be added to the current segment.
From https://www.w3.org/TR/css-text-3/#cursive-script:
Cursive scripts do not admit gaps between their letters for either justification
or letter-spacing. The following Unicode scripts are included: Arabic, Hanifi
Rohingya, Mandaic, Mongolian, N’Ko, Phags Pa, Syriac