Regex excluding specific characters

For that specific lesson, the correct regex is:

[^b]og

EXPLANATION:

/[^b]og/

[^b] match a single character not present in the list below
b the literal character b (case sensitive)
og matches the characters og literally (case sensitive)

NOTES:

Negated Character Classes

Typing a caret after the opening square bracket negates the character
class. The result is that the character class matches any character
that is not in the character class. Unlike the dot, negated character
classes also match (invisible) line break characters. If you don’t
want a negated character class to match line breaks, you need to
include the line break characters in the class. [^0-9\r\n] matches any
character that is not a digit or a line break.

It is important to remember that a negated character class still must
match a character. q[^u] does not mean: “a q not followed by a u“. It
means: “a q followed by a character that is not a u“. It does not
match the q in the string Iraq. It does match the q and the space
after the q in Iraq is a country. Indeed: the space becomes part of
the overall match, because it is the “character that is not a u” that
is matched by the negated character class in the above regexp. If you
want the regex to match the q, and only the q, in both strings, you
need to use negative lookahead.