Function charAt

scripts/verify.cjs:32–36

(lines, x, y)

function isVBorder(ch) { return V_BORDERS.has(ch); }

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

function verify(text) {
  const lines = text.split('\n');