Added docs for C<while> and C<until>

lib/Language/control.pod

@@ -452,6 +452,64 @@ is equivalent to the C-ish idiom:
 
     loop (;;) {...}
 
+=head2 while, until
+
+The C<while> statement executes the block as long as its condition is
+true. So
+
+=begin code
+
+my $x = 1;
+while $x < 4 {
+print $x++;
+}
+print "\n";
+
+=end code
+
+produces
+
+=begin code
+
+123
+
+=end code
+
+Similarly, the C<until> statement executes the block as long as the
+expression is false.
+
+=begin code
+
+my $x = 1;
+until $x > 3 {
+print $x++;
+}
+print "\n";
+
+=end code
+
+again produces
+
+=begin code
+
+123
+
+=end code
+
+The condition for C<while> or C<until> can be parenthesized, but there
+must be a space between the keyword and the opening parenthesis of the
+condition.
+
+Both C<while> and C<until> can be used as statement modifiers. E. g.
+
+=begin code
+
+$x++ while $x < 12
+
+=end code
+
+Also see C<repeat/while> and C<repeat/until> below.
+
 =head2 repeat/while, repeat/until
 
 Perl 5 allows one to apply a statement modifier to a C<do> block such that