ConstReadonlyAboveBaseline: 1Sit the placeholder on top of the baseline.
ReadonlyBaseline: 0Line the placeholder's own baseline up with the text's.
ReadonlyBelowBaseline: 2Hang the placeholder below the baseline.
ReadonlyBottom: 4Align its bottom edge with the line's bottom.
ReadonlyMiddle: 5Centre it against the line.
ReadonlyTop: 3Align its top edge with the line's top.
How a placeholder sits against the line it interrupts.
Passed to ParagraphBuilder.addPlaceholder; the numbering is CanvasKit's.
🧪 Not in the HTML Canvas standard.