line_insert
LINE *line_insert(LINE *line, const char *string, int len);
line = line_insert(line, text_buffer, len);
line = line_insert(line, "\n", 1);
line_insert(line, "\n", 1);
line_insert(tail->prev, "\n", 1);
line_insert(line, location, length_of(location));
line = line_insert(line, line_buffer, ret);