/* Clear searchbox-input field */
function clear_text() {
    var search_input = document.getElementById("keyword");
    if (search_input.value == 'zoek op trefwoord') {
        search_input.value = "";
        document.getElementById("keyword").style.textAlign = "left";
    }
}

/* Set default text in searchbox-input field */
function set_text() {
    var search_input = document.getElementById("keyword");
    if (search_input.value == '') {
        search_input.value = "zoek op trefwoord";
        document.getElementById("keyword").style.textAlign = "center";
    }
}

/* menu items - images changing */
function set_image(id) {        
        var hidden_pic = document.getElementById("pic"+id);
        document.getElementById("default_content").style.display = 'none';
        hidden_pic.style.display = "block";
}

function unset_image(pic,id) {
       var hidden_pic = document.getElementById("pic"+id);
       hidden_pic.style.display = "none";
       document.getElementById("default_content").style.display = 'block';
}