Minor clean-up (misplaced X<> header and footnote) (#2356)

Author: threadless-screw

doc/Language/syntax.pod6

@@ -221,8 +221,7 @@ of comment
 say 'code again';
 =end code
 
-X<identifier>
-=head2 Identifiers
+=head2 X<Identifiers|identifier, identifiers>
 
 Identifiers are grammatical building blocks that may be used to give a name
 to entities/objects such as constants, variables (e.g. Scalars) and routines
@@ -308,7 +307,9 @@ generates unique variants of that identifier.
 These strings have the form C<:key<value>>, wherein C<key> I<or> C<value> are
 optional; that is, after the colon that separates it from a regular identifier,
 there will be a C<key> and/or a quoting bracketing construct such as C«< >», C<« »>
-or C<[' ']> which quotes one or more arbitrary characters C<value>:
+or C<[' ']> which quotes one or more arbitrary characters C<value>: N<Starting
+with Perl 6 language version 6.d, colon pairs with C<sym> as the C<key>
+(e.g. C«:sym<foo>») are reserved for possible future use.>
 
 =begin code :skip-test<Identifiers good and bad>
 # exemplary valid extended identifiers:
@@ -323,8 +324,6 @@ party:16sweet
 party:!a                  # ...and neither is !a
 party:$a                  # ...nor $a
 =end code
-N<Starting with Perl 6 language version 6.d, colon pairs with C<sym> as the
-C<key> (e.g. C«:sym<foo>») are reserved for possible future use.>
 
 In an extended identifier, the postfix string is considered an integral part of
 the name, so C<infix:<+>> and C<infix:<->> are two different operators. The