PDFs carry no underline font flag — underlines are stroked horizontal
lines or thin filled rects drawn under the baseline. Correlate those
graphics (already parsed from the content stream) with text items in a
post-pass: a rule within ~0.35em below the baseline covering >=60% of
an item's width marks is_underline.
Exposed through the napi and python bindings. Verified on real docs:
4/4 underlined sentences flagged on a Japanese report, links/headings
flagged on 8 of 10 underline-bearing eval docs, zero flags on docs
without underlines. Known FP source (table cell borders) documented —
downstream applies inline styling only to plain-text regions.
napi 1.9.8 -> 1.9.9.
Co-authored-by: Cursor <cursoragent@cursor.com>
