One glyph of shaped text, as Pica.shape/3 returns it. Every length is in font units, or at the scale shaping was given, rounded to a whole unit as HarfBuzz rounds it.

• :glyph_id — which of the font's glyphs it is; 0, .notdef, for a character the font lacks. An invisible character, such as a soft hyphen, is the font's space glyph, advancing 0 (see Pica.shape/3).
• :cluster — where in the text it came from: the index, counting characters (Unicode code points) from 0, of the first character of the cluster it belongs to. A cluster is the smallest run of characters and glyphs that shaping keeps together: a ligature for "ffi" carries the cluster of its first "f", and an accent joined to its letter carries the letter's. Clusters rise along left-to-right text and fall along right-to-left text, since glyphs come back in the order they are drawn, from left to right.
• :x_advance — how far the glyph moves the pen on once shaping has positioned it, kerning included. A mark that sits on the glyph before it, such as a combining accent, advances 0.
• :nominal_advance — the glyph's advance as the font stores it, before shaping adjusted it, as Pica.nominal_advances/2 gives it. Less :x_advance, it is what shaping took off or added, such as kerning.
• :x_offset, :y_offset — how far the glyph is drawn from where the pen stands, without moving the pen, with y rising upward: how an accent is placed over its letter.