Better tag some skip-tests, and allow some to run

doc/Language/5to6-nutshell.pod6

@@ -1526,7 +1526,7 @@ C<is export> role on the relevant subs and I<all> subs with this role are
 then exported.  Hence, the following module C<Bar> exports the subs C<foo>
 and C<bar> but not C<baz>:
 
-=begin code :skip-test
+=begin code :skip-test<unit>
 unit module Bar;
 
 sub foo($a) is export { say "foo $a" }

doc/Language/classtut.pod6

@@ -316,7 +316,7 @@ possible to predict the moment when attribute initialization will be executed,
 because it can take place during compilation, runtime or both, especially when
 importing the class using the L<use|/syntax/use> keyword.
 
-    =begin code :skip-test
+    =begin code :preamble<class Foo {}; sub some_complicated_subroutine {}>
     class HaveStaticAttr {
           my Foo $.foo = some_complicated_subroutine;
     }
@@ -493,7 +493,7 @@ After creating a class, you can create instances of the class.  Declaring a
 custom constructor provides a simple way of declaring tasks along with their
 dependencies. To create a single task with no dependencies, write:
 
-=for code :skip-test
+=for code :preamble<class Task {}>
 my $eat = Task.new({ say 'eating dinner. NOM!' });
 
 An earlier section explained that declaring the class C<Task> installed a
@@ -505,7 +505,7 @@ modifying or accessing an existing object.
 
 Unfortunately, dinner never magically happens.  It has dependent tasks:
 
-    =begin code :skip-test
+    =begin code :preamble<class Task {}>
     my $eat =
         Task.new({ say 'eating dinner. NOM!' },
             Task.new({ say 'making dinner' },
@@ -523,7 +523,7 @@ Notice how the custom constructor and sensible use of whitespace makes task depe
 Finally, the C<perform> method call recursively calls the C<perform> method
 on the various other dependencies in order, giving the output:
 
-    =begin code :skip-test
+    =begin code :lang<output>
     making some money
     going to the store
     buying food
@@ -563,7 +563,7 @@ other means, such as attribute accessors.
 Now, any object of type Programmer can make use of the methods and accessors
 defined in the Employee class as though they were from the Programmer class.
 
-    =begin code :skip-test
+    =begin code :preamble<class Programmer {}>
     my $programmer = Programmer.new(
         salary => 100_000,
         known_languages => <Perl5 Perl6 Erlang C++>,
@@ -580,7 +580,7 @@ Of course, classes can override methods and attributes defined by parent
 classes by defining their own.  The example below demonstrates the C<Baker>
 class overriding the C<Cook>'s C<cook> method.
 
-    =begin code :skip-test
+    =begin code :preamble<class Employee {}>
     class Cook is Employee {
         has @.utensils  is rw;
         has @.cookbooks is rw;
@@ -636,7 +636,7 @@ classes when looking up a method to search for.  Perl 6 uses the L<C3 algorithm
 multiple inheritance hierarchies, which is better than depth-first search
 for handling multiple inheritance.
 
-    =begin code :skip-test
+    =begin code :preamble<class Programmer {}; class Cook {}>
     class GeekCook is Programmer is Cook {
         method new( *%params ) {
             push( %params<cookbooks>, "Cooking for Geeks" );
@@ -671,7 +671,7 @@ Classes to be inherited from can be listed in the class declaration body by
 prefixing the C<is> trait with C<also>. This also works for the role
 composition trait C<does>.
 
-    =begin code :skip-test
+    =begin code :preamble<class Programmer {}; class Cook {}>
     class GeekCook {
         also is Programmer;
         also is Cook;
@@ -692,7 +692,7 @@ a controlling object) for some properties, such as its type.
 Given an object C<$o> and the class definitions from the previous sections,
 we can ask it a few questions:
 
-    =begin code :skip-test
+    =begin code :preamble<my $o; class Employee {}; class GeekCook {}>
     if $o ~~ Employee { say "It's an employee" };
     if $o ~~ GeekCook { say "It's a geeky cook" };
     say $o.perl;
@@ -702,7 +702,7 @@ we can ask it a few questions:
 
 The output can look like this:
 
-    =begin code :skip-test
+    =begin code :lang<output>
     It's an employee
     (Programmer)
     Programmer.new(known_languages => ["Perl", "Python", "Pascal"],
@@ -736,7 +736,7 @@ it is actually a method call on its I<meta class>, which is a class managing
 the properties of the C<Programmer> class – or any other class you are
 interested in. This meta class enables other ways of introspection too:
 
-=for code :skip-test
+=for code :preamble<my $o>
 say $o.^attributes.join(', ');
 say $o.^parents.map({ $_.^name }).join(', ');
 

doc/Language/control.pod6

@@ -69,14 +69,14 @@ you would normally put semicolon, then you do not need the semicolon:
 
 ...but:
 
-=begin code :skip-test
+=begin code :skip-test<syntax error>
 { 42.say }  { 43.say }    # Syntax error
 { 42.say; } { 43.say }    # Also a syntax error, of course
 =end code
 
 So, be careful when you backspace in a line-wrapping editor:
 
-=begin code :skip-test
+=begin code :skip-test<syntax error>
 { "Without semicolons line-wrapping can be a bit treacherous.".say } \
 { 43.say } # Syntax error
 =end code
@@ -119,7 +119,7 @@ parenthesize a statement if it is the last thing in an expression:
 =for code
 3, do if 1 { 2 }  ; # OUTPUT: «(3, 2)␤»
 3,   (if 1 { 2 }) ; # OUTPUT: «(3, 2)␤»
-=for code :skip-test
+=for code :skip-test<syntax error>
 3,    if 1 { 2 }  ; # Syntax error
 
 ...which brings us to C<if>.
@@ -135,7 +135,7 @@ instead the C<{> and C<}> around the block are mandatory:
 
 =for code
 if 1 { "1 is true".say }  ; # says "1 is true"
-=for code :skip-test
+=for code :skip-test<syntax error>
 if 1   "1 is true".say    ; # syntax error, missing block
 =for code
 if 0 { "0 is true".say }  ; # does not say anything, because 0 is false
@@ -190,7 +190,7 @@ if 0 { say "no" } else{ say "yes" }    ; # says "yes", space is not required
 The C<else> cannot be separated from the conditional statement by a
 semicolon, but as a special case, it is OK to have a newline.
 
-=for code :skip-test
+=for code :skip-test<syntax error>
 if 0 { say "no" }; else { say "yes" }  ; # syntax error
 =for code
 if 0 { say "no" }
@@ -213,14 +213,16 @@ be run.  You can end with an C<elsif> instead of an C<else> if you want.
 
 You cannot use the statement modifier form with C<else> or C<elsif>:
 
-=for code :skip-test
+=for code :skip-test<syntax error>
 42.say if 0 else { 43.say }            # syntax error
 
 All the same rules for semicolons and newlines apply, consistently
 
-=for code :skip-test
+=for code :skip-test<syntax error>
 if 0 { say 0 }; elsif 1 { say 1 }  else { say "how?" } ; # syntax error
 if 0 { say 0 }  elsif 1 { say 1 }; else { say "how?" } ; # syntax error
+
+=for code
 if 0 { say 0 }  elsif 1 { say 1 }  else { say "how?" } ; # says "1"
 
     if 0 { say 0 } elsif 1 { say 1 }
@@ -261,7 +263,7 @@ two differences C<unless> works the same as L<#if>:
 
 =for code
 unless 1 { "1 is false".say }  ; # does not say anything, since 1 is true
-=for code :skip-test
+=for code :skip-test<syntax error>
 unless 1   "1 is false".say    ; # syntax error, missing block
 =for code
 unless 0 { "0 is false".say }  ; # says "0 is false"

doc/Language/functions.pod6

@@ -370,7 +370,7 @@ an un-named C<Capture> parameter, and allows a C<multi> to take additional
 arguments. The first two calls succeed, but the third fails (at compile time)
 because C<42> doesn't match C<Str>.
 
-=for code :skip-test
+=for code :preamble<sub congratulate {}>
 say &congratulate.signature # OUTPUT: «(Str $reason, Str $name, | is raw)␤»
 
 You can give the C<proto> a function body, and place the C<{*}> where
@@ -394,7 +394,7 @@ with. Parameter defaults and type coercions will work but are not passed on.
 proto mistake-proto(Str() $str, Int $number = 42) {*}
 multi mistake-proto($str, $number) { say $str.^name }
 mistake-proto(7, 42);  # OUTPUT: «Int␤» -- not passed on
-=for code :skip-test
+=for code :skip-test<compilation error>
 mistake-proto('test'); # fails -- not passed on
 
 =head2 X<only|declarator>