Revises text and closes #2704

Author: JJ

doc/Language/syntax.pod6

@@ -583,9 +583,9 @@ or an explicit base in adverbial notation like C<< :16<A0> >> specifies it
 otherwise. Unlike other programming languages, leading zeros do I<not> indicate
 base 8; instead a compile-time warning is issued.
 
-In all literal formats, you can use underscores to group digits; they
-don't carry any semantic information; the following literals all
-evaluate to the same number:
+In all literal formats, you can use underscores to group digits, although they
+don't carry any semantic information; the following literals all evaluate to the
+same number:
 
 =begin code :skip-test
 1000000
@@ -594,21 +594,21 @@ evaluate to the same number:
 100_00_00
 =end code
 
-=head4 Int literals
+=head4 C<Int> literals
 
 Integers default to signed base-10, but you can use other bases. For details,
 see L<Int|/type/Int>.
 
 =begin code :skip-test
-# actually not a literal, but unary - operator applied to numeric literal 2
+# not a single literal, but unary - operator applied to numeric literal 2
 -2
 12345
 0xBEEF      # base 16
 0o755       # base 8
 :3<1201>    # arbitrary base, here base 3
 =end code
 
-=head4 Rat literals
+=head4 C<Rat> literals
 
 L<Rat|/type/Rat> literals (rationals) are very common, and take the
 place of decimals or floats in many other languages. Integer division
@@ -623,7 +623,7 @@ also results in a C<Rat>.
     2/3         # Not actually a literal, but still a Rat
     =end code
 
-=head4 Num literals
+=head4 C<Num> literals
 
 Scientific notation with an integer exponent to base ten after an C<e> produces
 L<floating point number|/type/Num>:
@@ -636,7 +636,7 @@ L<floating point number|/type/Num>:
     2e2.5       # error
     =end code
 
-=head4 Complex literals
+=head4 C<Complex> literals
 
 L<Complex|/type/Complex> numbers are written either as an imaginary number
 (which is just a rational number with postfix C<i> appended), or as a sum of
@@ -648,7 +648,7 @@ a real and an imaginary number:
     =end code
 
 X<|Pairs (literals)>
-=head3 Pair literals
+=head3 X<Pair literals>
 
 L<Pairs|/type/Pair> are made of a key and a value, and there are two
 basic forms for constructing them: C<< key => 'value' >> and