returned index if it's larger than M-1, in case of X, Y, S, A

https://fityk.nieto.pl/data.html#data-point-transformations says:

• x, y, s, a [...] If the index is less than 0 or larger than M-1, the value for the first or the last point, respectively, is returned.
• For X, Y, S, A [...] If the index is less than 0 or larger than M-1, 0 is returned.

but in my tests, Y[index>=M] returns Y[M-1], just like y

Can I assume it's just error in doc? if so, I can fix it myself (I'm preparing many small changes in docs)