Measured against documents re-saved by other software. A line's height is rounded to whole
pixels (halves up) with the baseline keeping its fraction inside it; a glyph's advance and its
kerning are each rounded to 1/1024 em before scaling; a line's width and wrapping leave out the
letter spacing after its last visible glyph. Rule tests on built-in fonts, a local-only check over
such documents, and three behaviour expectations updated to the new rules.
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