def find_diff_start(old_src, new_src):
    """Find line number and column number where text first differs."""
    old_lines = old_src.split("\n")
    new_lines = new_src.split("\n")

    for line in range(min(len(old_lines), len(new_lines))):
        old = old_lines[line]
        new = new_lines[line]
        if old == new:
            continue
        for col in range(min(len(old), len(new))):
            if old[col] != new[col]:
                return line, col
        # Difference at the end of the line...
        return line, min(len(old), len(new))
    # Difference at the end of the file...
    return min(len(old_lines), len(new_lines)), 0