$(document).ready(function() {

  $(document).click(function(event) {

    //    showText(event.target, $("input[id$='txtSearch']"));
    //    showText(event.target, $("input[id$='txtEmail']"));

  var controlsWithText = $(".txtShowHideText");
    $.each(controlsWithText, function() {
      showText(event.target, this);
    });

  });

  $(".txtShowHideText").click(function(event) {
    $(this).val("");
  });
});

function showText(eventTarget, txtControl) {
  if (eventTarget != txtControl && eventTarget.className != "knop") {
    txtControl.value = txtControl.defaultValue;
  }
}