Documents X::NYI constructor and methods

Closes #2052

Author: JJ

doc/Type/X/NYI.pod6

@@ -10,7 +10,7 @@ Error class for unimplemented features. I<NYI> stands for I<Not Yet
 Implemented>.
 
 If a Perl 6 compiler is not yet feature complete, it may throw an C<X::NYI>
-exception when a program uses a feature that it can detect is not yet
+exception when a program uses a feature that it can detect and is somehow specified is not yet
 implemented.
 
 A full-featured Perl 6 compiler must not throw such exceptions, but
@@ -23,8 +23,52 @@ HyperWhatever is not yet implemented. Sorry.
 
 =head1 Methods
 
-=head2 method features
+=head2 method new
+
+    method new( :$feature, :$did-you-mean, :$workaround)
+
+This is the default constructor for C<X:NYI> which can take three parameters with obvious meanings.
+
+=begin code
+class Nothing {
+    method ventured( $sub, **@args) {
+        X::NYI.new( feature => &?ROUTINE.name,
+                    did-you-mean => "gained",
+                    workaround => "Implement it yourself" ).throw;
+    }
+}
+
+my $nothing = Nothing.new;
+$nothing.ventured("Nothing", "Gained");
+=end code
+
+In this case, we are throwing an exception that indicates that the C<ventured> routine has not been implemented; we use the generic C<&?ROUTINE.name> to not tie the exception to the method name in case it is changed later on. This code effectively throws this exception
+
+=begin code
+# OUTPUT:
+# ventured not yet implemented. Sorry.
+# Did you mean: gained?
+# Workaround: Implement it yourself
+#   in method ventured at NYI.p6 line 6
+#   in block <unit> at NYI.p6 line 14
+=end code
+
+Using the exception properties, it composes the message that we see there.
+
+=head2 method feature
 
 Returns a C<Str> describing the missing feature.
 
+=head2 method did-you-mean
+
+Returns a C<Str> indicating the optional feature that is already implemented.
+
+=head2 method workaround
+
+It helpfully shows a possible workaround for the missing feature, if it's been declared.
+
+=head2 method message
+
+Returns the message including the above properties.
+
 =end pod