Module faces 

Face management: the engine’s face roster, character→glyph resolution with the TeX math-italic convention and the math-alphabet mappings, and glyph-metric queries in em units.

Multi-face layout is structural (G0-3 Verdict 3): ∑ ∫ ∏ do not exist in CM Unicode and resolve through the math-symbol fallback face, so every positioned glyph names its face and resolution is data, not a rendering afterthought. Resolution walks a per-request preference chain and falls back across the roster; a character no face maps is a precise MathError::UnmappedChar.

Italic correction, synthesized. TFM italic corrections do not exist in the sfnt world; per the ratified measure-and-validate seam they are synthesized from decoded geometry as the ink’s right overhang past the advance (max(0, bbox_xmax − advance)), which reproduces their role in script placement (slanted ∫ and italic letters push superscripts right).

Structs

FaceSet

The engine’s face roster, in FaceId order. The set mirrors the bundled sovereign default (§11.1): CM regular/italic/bold/bold-italic, CM Typewriter, a sans face, and the math-symbol coverage face.

GlyphMetrics

Per-glyph metrics in ems of the face’s design size.

Constants

FACE_BOLD

FaceId of CM Bold.

FACE_BOLD_ITALIC

FaceId of CM Bold Italic.

FACE_ITALIC

FaceId of CM Italic (math letters, lowercase Greek).

FACE_REGULAR

FaceId of CM Regular (upright letters, digits, most symbols).

FACE_SANS

FaceId of the sans face (IBM Plex Sans).

FACE_SYMBOLS

FaceId of the math-symbol coverage face (Noto Sans Math subset).

FACE_TYPEWRITER

FaceId of CM Typewriter.

Functions

accent_spacing_fallback

Spacing fallbacks for combining accent marks: when a face maps neither the combining character nor anything in the chain, the spacing equivalent often exists (CM Unicode carries the spacing accents).

alphabet_map

Map a character under a math alphabet, returning the (possibly remapped) character and its face-preference chain. Blackboard and calligraphic go through the Unicode math-alphanumeric planes (with the Letterlike exceptions), which the symbol face covers; the styled text faces handle the rest.

blackboard_char

The double-struck (blackboard) codepoint of a character: the Letterlike exceptions first, then U+1D538-block letters and U+1D7D8-block digits; unmapped characters pass through (and then fail resolution precisely).

calligraphic_char

The script (calligraphic) codepoint of a character, with the Letterlike exceptions.

char_alternate

Documented glyph alternates, applied only when the exact character is unmapped across the whole roster: variant forms whose conventional glyph the bundled faces do carry. The substitution stops firing the moment a face gains the exact codepoint (miss-only), and every pair is a same-letter variant — different-but-fine territory, not a semantic change.

default_math_chain

The TeX math-italic convention for a direct character with no alphabet override: Latin letters and lowercase Greek render from the italic face; everything else (digits, uppercase Greek, operators, symbols) from the regular face — with the roster as fallback either way.

glyph_metrics

Measure a glyph in em units.

kern_em

Kerning between two glyphs of one face, in ems.