Add support for stmaryrd

[pkra]

• Add support for the actual font
• Add TeX macros from the stmaryrd package.

[pkra]

The TeX macros could easily start as a third party extension right away.

[jeanas]

One special case is integer interval brackets, which have double bars, resembling [[𝑎,𝑏]] or [| a, b|]
In stmaryrd, these are provided as \llbracket and rrbracket. They can be mimicked using [\![a, b]\!] but it looks ugly in subscripts.
They are somewhat special since they are the only commands in stmaryrd that can work with \left and \right (see the documentation of stmaryrd). Since they are more common than the other symbols contained in this package, I would humbly suggest to make them available in the base package.

[dpvc]

@jean-abou-samra, we will be working on expanding the font support in MathJax v3 during this coming summer. That will make it easier to top the things you are asking for.

[contradictioned]

Sorry to dig this up, but is stmaryrd really supported? Especially w.r.t. \llbracket and \rrbracket I didn't manage to get this running.

[pkra]

is stmaryrd really supported?

No it isn't (though I have a draft for a third party extension somewhere that could become open source).

Much of the St Mary Rd font is covered by Unicode nowadays so with a good font (e.g., v4) you can just map them to Unicode positions. E.g., https://github.com/AmerMathSoc/mathjax-unicode-math does a ton of that, including llbracket, rrbracket.

[contradictioned]

Ok, thanks for the clarification :)

[pkra]

Happy to help. Feel free to ping me by email to see if I can get the extension into a publishable state.