Significance brackets from a precomputed test table — ggpubr’s
stat_pvalue_manual() / geom_bracket(data = test_table). Nothing is
recomputed: every bracket comes from one table row.
Significance bracket — a horizontal bar with two downward end ticks spanning
[xmin, xmax] at height y, captioned with a label above it (R’s
ggpubr::geom_bracket). Typically annotates a pairwise-comparison p-value or
significance stars over a boxplot.