\perp is mapped to the wrong Unicode code point

[NSoiffer]

Issue Summary

MathJax maps the TeX macro \perp to the Unicode char U+22A5 which Unicode defines as "UP TACK {base, bottom}". It should be mapped to U+27C2 which Unicode defines as "PERPENDICULAR {orthogonal to}". Although they look similar, they are slightly different.

Beside the potential subtle difference in rendering, the bad mapping means that screen readers will say the wrong thing for \perp unless they (wrongly) map U+22A5 to "perpendicular". If they do that, then they won't speak "up tack" or "bottom" when they should.

Steps to Reproduce:

The bad mapping is in the code in several places. If you want to check the output, you can

1. open https://mathjax.github.io/MathJax-demos-web/input-tex2chtml.html
2. Enter x \perp y
3. Right click in the rendered result and choose "Show Math As: MathML Code"

Technical details:

• MathJax Version: in master branch and v4.0-beta

[dpvc]

This goes way back to version 1, and is due to the fact that the original MathJax fonts didn't include a glyph for U+27C2, and to the fact that I didn't know Unicode very well at that time, and that MathJax had not yet become involved in assistive technology.

It should probably be changed for v4.

[NSoiffer]

That seems to be the case for many other translators including KaTeX and pandoc. I think everyone started with a similar mapping. I filed bug reports with them also.