Nominal text height (em size) in mm, for the writer to convert to points.
The model distance this label marks, in metres, or null for free text
such as the ratio. A consumer can multiply it by the transform's
worldToMm and check that the label really sits there — which is what
makes "the bar is drawn to scale" a measurable claim rather than a hope.
The text BASELINE, which is where PDF text origins sit.
One text run of the stamp, in page millimetres from the page's top-left.