Function isVBorder

scripts/verify.cjs:30–30

(ch)

function isCorner(ch) { return CORNERS_ASCII.has(ch) || CORNERS_UNICODE.has(ch); }
function isHBorder(ch) { return H_BORDERS.has(ch); }
function isVBorder(ch) { return V_BORDERS.has(ch); }

function charAt(lines, x, y) {
  if (y < 0 || y >= lines.length) return '';