On https://en.wikipedia.org/wiki/Help:Displaying_a_formula I see that Mathoid generates
U+2216;∖ set minus
U+2225; ∥ parallel to
These are mathematical binary operators with very specific meaning but sometimes they are used in inappropriate context. For example it's correct that \setminus generates U+2216 but the more generic \backslash command should instead use "reverse solidus". Same with \| or \Vert which should generate "U+2016 double vertical line" when they are used as fences, not U+2225.
This obviously causes issue for assistive technologies. Also, this may result in wrong display for MathML rendering engines that rely on the values of the MathML Operator Dictionary (http://www.w3.org/TR/MathML3/appendixc.html).