function defineSymbol(mode, font, group, replace, name) {
	    module.exports[mode][name] = {
	        font: font,
	        group: group,
	        replace: replace,
	    };
	}
This file holds a list of all no-argument functions and single-character
symbols (like 'a' or ';').

For each of the symbols, there are three properties they can have:
- font (required): the font to be used for this symbol. Either "main" (the
	     normal font), or "ams" (the ams fonts).
- group (required): the ParseNode group type the symbol should have (i.e.
	     "textord", "mathord", etc).
	     See https://github.com/Khan/KaTeX/wiki/Examining-TeX#group-types
- replace: the character that this symbol or function should be
  replaced with (i.e. "\phi" has a replace value of "\u03d5", the phi
  character in the main font).

The outermost map in the table indicates what mode the symbols should be
accepted in (e.g. "math" or "text").