The secondary caret index, when different from the main caret
index, corresponds to the insert position when inserting text
at a direction change opposite to the layout's main text
direction.
This member contains the rotation angle of the caret in
degrees, with 0 denoting an unrotated caret (the unrotated
caret orientation depends on the writing mode, horizontally or
vertically). The rotation angle is positive for
counter-clockwise rotations.
