jQuery.getDocHeight = function(){
    return Math.max(
        jQuery(document).height(),
        jQuery(window).height(),
        /* For opera: */
        document.documentElement.clientHeight
    );
};

jQuery.fn.postcode = function() {
	this.defaultValue = "Type your postcode here";
	return this.focus(function() {
		if( this.value == this.defaultValue ) {
			this.value = "";
		}
	}).blur(function() {
		if( !this.value.length ) {
			this.value = this.defaultValue;
		}
	});
};