Adds Boolean contexts refs #1225

doc/Language/contexts.pod6

@@ -168,6 +168,31 @@ C<but> creates a mixin, which endows the complex number with a C<Str> method.
 C<put> contextualizes it into a string, that is, it calls C<Str>, the string
 contextualizer, with the result shown above.
 
+=head1 Boolean X<|Boolean context>
+
+This context will force a variable to be interpreted as C<True> or C<False>.
+
+    say "Hey" if 7;  # OUTPUT: «Hey␤»
+    say "Ahoi" if "";
+
+This context appears in expressions such as C<if> or C<while>, and is
+equivalent to calling C<so> on these values.
+
+=for code
+say "Hey" if 7.so;          # OUTPUT: «Hey␤»
+say "Ahoi" if not set().so; # OUTPUT: «Ahoi␤»
+
+In general, non-zero, non-empty will be converted to C<True>; zero or empty
+will be equivalent to False. But C<.so> can be defined to return any Boolean
+value we want, so this is just a rule ov thumb.
+
+C<?> and C<!> are the Boolean context operator and its negation. They will
+force this context on an object.
+
+=for code
+say ? 0i;    # OUTPUT: «False␤»
+say ! :true; # OUTPUT: «False␤»
+
 =end pod
 
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