Add a code comment

base/ltspace.dtx

@@ -1214,13 +1214,17 @@
 %   We need to keep \cs{@xobeysp} as it is widely used; so here it is
 %   let to the non-robust command \cs{nobreakspace }.
 %
+%   The fragile version of |~| needs a brace group after \cs{nobreakspace}
+%   to prevent loss of spaces if it occurs in an expansion context. That's
+%   not an issue with the updated \cs{protected} definition, so we keep the
+%   code shorter and avoid that.
 %    \begin{macrocode}
 \DeclareRobustCommand{\nobreakspace}{%
    \leavevmode\nobreak\ }
 \catcode `\~=13
 %</2ekernel>
 %<latexrelease>\IncludeInRelease{2023/11/01}%
-%<latexrelease>                 {[tilde]}{Protected tilde}%
+%<latexrelease>                 {\tilde}{Protected tilde}%
 %<*2ekernel|latexrelease>
 \protected\edef~{%
   \noexpand\ifincsname\noexpand\expandafter\string~%