wiki.techinc.nl/resources/jquery/jquery.placeholder.js

/**
 * HTML5 placeholder emulation for jQuery plugin
 *
 * This will automatically use the HTML5 placeholder attribute if supported, or emulate this behavior if not.
 *
 * @author Trevor Parscal <tparscal@wikimedia.org>
 * @author Krinkle <krinklemail@gmail.com>
 * @version 0.2.0
 * @license GPL v2
 */

$.fn.placeholder = function() {

	return this.each( function() {

		// If the HTML5 placeholder attribute is supported, use it
		if ( this.placeholder && 'placeholder' in document.createElement( this.tagName ) ) {
			return;
		}

		var placeholder = this.getAttribute('placeholder');
		var $input = $(this);

		// Show initially, if empty
		if ( this.value === '' || this.value == placeholder ) {
			$input.addClass( 'placeholder' ).val( placeholder );
		}

		$input
			// Show on blur if empty
			.blur( function() {
				if ( this.value === '' ) {
					this.value = placeholder;
					$input.addClass( 'placeholder' );
				} else {
					$input.removeClass( 'placeholder' );
				}
			} )

			// Hide on focus
			.focus( function() {
				if ($input.hasClass('placeholder')) {
					this.value = '';
					$input.removeClass( 'placeholder' );
				}
			} );

		// Blank on submit -- prevents submitting with unintended value
		this.form && $( this.form ).submit( function() {
			// $input.trigger( 'focus' ); would be problematic
			// because it actually focuses $input, leading
			// to nasty behavior in mobile browsers
			if ( $input.hasClass('placeholder') ) {
				$input
					.val( '' )
					.removeClass( 'placeholder' );
			}
		});

	});
};