Set up the RegEx to be able to match characters between spoiler
characters (for now, the spoiler characters are > and <, so any text
between >these two symbols< will be matched by the RegEx. This is for
https://linear.app/comm/issue/ENG-1981/set-up-regex-to-match-text-between-two-spoiler-characters,
and subsequent parts of the task will be stacked on top of this diff.