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<p>Hi David</p>
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<p>Sure \textdir works in vertical mode in luatex but luatex's behavior is buggy. For instance, consider the following minimal example</p>
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<p>{\textdir TRT This} is just a test.</p>
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<p>\bye</p>
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<p>As you can see there is no indent at the beginning of the paragraph and that indent is shifted as a space between `This' and `is' which is completely wrong. So to fix it, you have to issue a \leavevmode at the start of the paragraph but by doing that, you
are already entering horizontal mode.</p>
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