function clear_field(dateField) {
dateField.value='';
}

function change_overflow(param,stav,vyska) {

if (stav=='visible') {
document.getElementById(param).style.height=vyska;
}

if (stav=='hidden') {
document.getElementById(param).style.height=vyska;
}

document.getElementById(param).style.overflow=stav;
}

function change_display(param,stav) {

if (stav=='visible') {
document.getElementById(param).style.display ='block';
var hght=document.body.scrollHeight;
document.getElementById('blacktransp').style.height = hght+'px';
}

if (stav=='hidden') {
document.getElementById(param).style.display ='none';
}

}