Checking around postfix calls

Rephrased `.:` which used *colonpair* (which is clearly
not). Eliminated index entry "postfix call" which didn't make a lot of
sense. And closes #1346, although that had been solved before.

doc/Language/operators.pod6

@@ -749,18 +749,18 @@ method call.
 =end code
 
 Technically, not a real operator; it's syntax special-cased in the compiler.
-X<|postfix call>
 
+X<|postfix call>
 =head2 postfix C«.:<prefix>»
 
-A prefix can be called like a method using colonpair notation. For example:
+An operator in prefix form can still be called like a method, that is, using the
+C<.> postfix notation, by preceding it by a colon. For example:
 
     my $a = 1;
     say ++$a;       # OUTPUT: «2␤»
     say $a.:<++>;   # OUTPUT: «3␤»
 
 Technically, not a real operator; it's syntax special-cased in the compiler.
-X<|prefix call>
 
 =head2 postfix C«.::»