How do I make an HTML text box show a hint when empty?

You can set the placeholder using the placeholder attribute in HTML (browser support). The font-style and color can be changed with CSS (although browser support is limited).

input[type=search]::-webkit-input-placeholder { /* Safari, Chrome(, Opera?) */
 color:gray;
 font-style:italic;
}
input[type=search]:-moz-placeholder { /* Firefox 18- */
 color:gray;
 font-style:italic;
}
input[type=search]::-moz-placeholder { /* Firefox 19+ */
 color:gray;
 font-style:italic;
}
input[type=search]:-ms-input-placeholder { /* IE (10+?) */
 color:gray;
 font-style:italic;
}

<input placeholder="Search" type="search" name="q">

That is known as a textbox watermark, and it is done via JavaScript.

• http://naspinski.net/post/Text-Input-Watermarks-using-Javascript-(IE-Compatible).aspx

or if you use jQuery, a much better approach:

• http://digitalbush.com/projects/watermark-input-plugin/
• or code.google.com/p/jquery-watermark

Another option, if you're happy to have this feature only for newer browsers, is to use the support offered by HTML 5's placeholder attribute:

<input name="email" placeholder="Email Address">

In the absence of any styles, in Chrome this looks like:

You can try demos out here and in HTML5 Placeholder Styling with CSS.

Be sure to check the browser compatibility of this feature. Support in Firefox was added in 3.7. Chrome is fine. Internet Explorer only added support in 10. If you target a browser that does not support input placeholders, you can use a jQuery plugin called jQuery HTML5 Placeholder, and then just add the following JavaScript code to enable it.

$('input[placeholder], textarea[placeholder]').placeholder();

You can add and remove a special CSS class and modify the input value onfocus/onblur with JavaScript:

<input type="text" class="hint" value="Search..."
    onfocus="if (this.className=='hint') { this.className = ''; this.value = ''; }"
    onblur="if (this.value == '') { this.className = 'hint'; this.value = 'Search...'; }">

Then specify a hint class with the styling you want in your CSS for example:

input.hint {
    color: grey;
}