Module atom 

The atom engine: TeX’s eight atom classes, contextual Bin→Ord degradation, and the inter-atom spacing table.

Everything here is TeX’s published mathematics (The TeXbook, chapter 17 and appendix G): the spacing table is transcribed entry-for-entry from page 170, and the two degradation rules are appendix G’s rules 5 and 6. These tables are the normative contract the spacing fixtures lock.

Enums

AtomClass

TeX’s eight atom classes.

PairSpacing

One entry of the spacing table.

Spacing

The amount of glue between two adjacent atoms.

Constants

ATOM_CLASSES

The eight classes in table order (the order of the spacing table’s rows and columns).

SPACING_TABLE

The inter-atom spacing table, exactly as published (The TeXbook, p. 170). Rows are the left atom’s class, columns the right atom’s class, both in ATOM_CLASSES order.

Functions

char_class

The intrinsic atom class of a direct character in math mode, before any command mapping. Follows plain TeX’s mathcode assignments.

classify_list

Classify a horizontal list: every item’s effective atom class, with TeX’s Bin→Ord degradation rules applied (appendix G, rules 5, 6, and 7):

intrinsic_class

The intrinsic atom class a node contributes to its enclosing list, or None for non-atom items (spacing, ties, breaks, alignment tabs, and the style/color markers), which are transparent to both degradation and inter-atom spacing.

pair_spacing

The raw table entry for a pair.

spacing_in_style

The glue between two adjacent atoms in a given style, with the script suppression rule applied. Impossible pairs yield no space (the engine never produces them after degradation; tolerating them here keeps the function total for untrusted callers).