add updide-down example

example/upside-down.php

@@ -0,0 +1,16 @@
+<?php
+/* Demonstration of upside-down printing */
+require __DIR__ . '/../vendor/autoload.php';
+use Mike42\Escpos\Printer;
+use Mike42\Escpos\PrintConnectors\FilePrintConnector;
+
+$connector = new FilePrintConnector("php://stdout");
+$printer = new Printer($connector);
+
+// Most simple example
+$printer -> text("Hello\n");
+$printer -> setUpsideDown(true);
+$printer -> text("World\n");
+$printer -> cut();
+$printer -> close();
+

src/Mike42/Escpos/Printer.php

@@ -966,9 +966,8 @@ public function setUnderline(int $underline = Printer::UNDERLINE_SINGLE)
      *
      * @param boolean $on True to enable, false to disable.
      */
-    public function setUpsideDown($on = true)
+    public function setUpsideDown(bool $on = true)
     {
-        self::validateBoolean($on, __FUNCTION__);
         $this -> connector -> write(self::ESC . "{" . ($on ? chr(1) : chr(0)));
     }