For horizontally written text, the text alignment is always visually left-aligned (that is, left-to-right and right-to-left are treated uniformly). For vertical text, this is equivalent to kCMTextMarkupAlignmentType_Start.
Mac Catalyst 13.0+Beta
While readers should be prepared to account for kCMTextMarkupAlignmentType_Left being equivalent to kCMTextMarkupAlignmentType_Start for vertical text, authors are discouraged from using kCMTextMarkupAlignmentType_Left for vertical text.
This documentation contains preliminary information about an API or technology in development. This information is subject to change, and software implemented according to this documentation should be tested with final operating system software.