How does the MATLAB symvar function work?

I read the documentation and help about the symvar function but I'm still confused about how it works, especially for the following example:

clc
clear all
syms x y a
symvar(x + y, 1)

When I run this M-file, I get the answer 'x'. Why am I getting this answer? Why not 'y'? And what is the role of the number 1 written as the second argument?

Answer 1

[Walter Roberson]

"symvar(s,n) chooses the n symbolic variables in s that are alphabetically closest to x and returns them in alphabetical order."

You get 1 because you asked for only 1.

You get x because it is alphabetically closer to x than y is