A token can be of type:
literal: the value is the character this token represents. This can be a combination of Unicode codepoints, for example for emojis.
_: superscript and subscript commands.
command: a command such as
}: begin and end group (use for arguments of commands and for grouping)
placeholder: a placeholder value meant to be replaced by some actual value
space: one or more space characters (including tab, etc...)