Bracket

An atom with left/right fences fitted to its complete body. Middle delimiters use the same measured extent and do not enlarge their own sizing target.

Property	Default	Meaning
children	Empty	Body elements or TeX source; with middle delimiters, one run per interval.
delim	"round"	Named pair: round, square, curly, or angle.
left_delim / right_delim	Named pair	Individual glyphs/commands; null omits a fence, while "." reserves TeX null-delimiter space.
middle	Absent	One delimiter string, or an array separating the body runs.
level	Automatic	Fixed level from 1 to 4, corresponding to big through Bigg.
delimiter_height	Body extent	Fixed requested height as a Gum length; use this or level.
style / size_index	Inherited	Math style and optional TeX size index.
klass / left / right	"minner"	Classes exposed to the surrounding row.

TeX \left…\middle…\right uses the same group measurement. Nested groups measure independently. \big, \Big, \bigg, \Bigg, and their l/m/r variants select fixed delimiter levels and the corresponding atom classes.

Missing glyphs in a Size font are skipped. Beyond the largest available glyph, ordinary fences scale uniformly; vertical bars preserve their width. Extensible piece assembly is not implemented. See math authoring.