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Vertical Substitution Feature Type

The vertical substitution feature type (kVerticalSubstitutionType) specifies that certain glyphs (such as parentheses) should change their appearance in vertical runs of text. Figure B-23 illustrates how vertical substitution works. The top line shows horizontal text—a word enclosed in parentheses. When the text is displayed vertically without turning on vertical substitution (left side of the figure), the parentheses appear odd. When vertical substitution is turned on (right side of the figure) the parentheses appear in the appropriate orientation.

If the font supports the vertical substitution feature type, its default behavior is to perform such substitutions. You may either prevent the substitution or allow it to occur. For vertical substitution to work, the vertically rotated forms must exist in the font and must be indicated as such in the font’s tables. Otherwise, no characters are substituted even when you turn on this feature explicitly. Note that vertical substitution is not used to rotate glyphs, simply to substitute forms, as shown in Figure B-23.

Table B-29 lists the selectors for the vertical substitution feature type. It is a contextual feature.

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