Why does not the current version of MathJax support \delimiterfactor?

How to verify, which version of MathJax is used here? It seems that v. 2.5 is not implemented yet. It has very useful features, as \delimiterfactor, which is needed here: https://tex.stackexchange.com/questions/284809/getting-large-braces-in-mathjax

MathJax does not implement the \delimiterfactor control sequence, but does have an internal value for delimiterfactor (the default value of 901 from TeX) that it uses in its computations for stretchy delimiters. That value can be set from Javascript, but not from within a TeX expression. One reason for this is that MathJax doesn't implement the localization of changes within braces, so changes to \delimiterfactor would be global.
1. Right-click any formula, like this one: $\int_0^1 e^x\,dx$