%%% Double-circumflex trap

% Is there a difference between those two cases?

\number`\^^A
\number`^^A

% And how about this?

\number`\^^@
\number`^^@

In the case of '^^A' (character code 1), both lines yield the number 1, the
backslash character's presence before the double-circumflex doesn't influence
the result. In the second case, the first line yields 0, while the second
results in 32. The reason is that the character of the code 0 ('^^@') has the
associated category code `ignored' (9). Any character of the category 9 will
simply be omitted, except when there is a backslash immediately before it. If
there is no backslash, the very next character is considered, which is a code
32... Well, actually its end-line character, which is replaced by the
character of the code being a current value of \endlinechar, which is 13 by
default, and character 13 has a default category code 5, which is finally
converted to the character 32.

\end
