Correct doc. consistency.

l3kernel/l3expan.dtx

@@ -665,7 +665,7 @@
 %     This is the \TeX{} \tn{noexpand} primitive.  It only prevents
 %     expansion.  At the beginning of an |f|-type argument, a space
 %     \meta{token} is removed even if it appears as \cs{exp_not:N}
-%     \cs{c_space_token}.  In an |x|-expanding definition
+%     \cs{c_space_token}.  In an |e|-expanding definition
 %     (\cs{cs_new:Npe}), a macro parameter introduces an argument even
 %     if it appears as \cs{exp_not:N} |#| |1|.  This differs from
 %     \cs{exp_not:n}.