neilgee

This plugin adds support for placeholder text in browsers that don’t support this HTML5 feature including Internet Explorer 6.
The plugin just activates the placeholders.js script by James Allardice http://jamesallardice.github.io/Placeholders.js/
There is no further configuration required.
For HTML input elements use the placeholder attribute and add a value, this value is removed when a user inputs the field. http://coolestguidesontheplanet.com/add-a-label-into-a-text-input-field-in-a-html-form/#html5
The script is 4KB and is set to load in the footer and has no library dependencies.
<h3>Usage</h3>
Just activate the plugin which loads the script, their is no further configuration.

Placeholder Text

This plugin adds support for placeholder text in browsers that don't support this HTML5 feature.

Petermann

Add a class in the form field.
Example of use with <a href="https://wordpress.org/plugins/contact-form-7/" rel="ugc">Contact Form 7</a>:
<pre><code>[tel your-phone class:phone placeholder "Phone"]
</code></pre>
Listing of classes available for use.
<pre><code>('span.start, input.start').mff_mask('00/0000');
('span.date, input.date').mff_mask('00/00/0000');
('span.time, input.time').mff_mask('00:00:00');
('span.time2, input.time2').mff_mask('00:00');
('input.date_time').mff_mask('00/00/0000 00:00:00');
('input.date_time2').mff_mask('00/00/0000 00:00');
('input.cep').mff_mask('00000-000', { clearIfNotMatch: true });
('input.zip').mff_mask('00000');
('input.phone, input[name="phonebr"]').mff_mask(PhoneMaskBehavior, nonoOptions);
('input.phone_us').mff_mask('(000) 000-0000');
('input.taxid').mff_mask('00-0000000');
('input.ssn').mff_mask('000-00-0000');
('input.mixed').mff_mask('AAA 000-S0S');
('input.cpf').mff_mask('000.000.000-00', { reverse: true, clearIfNotMatch: true });
('input.cnpj').mff_mask('00.000.000/0000-00', { reverse: true, clearIfNotMatch: true });
('input.money').mff_mask('000.000.000.000.000,00', { reverse: true });
('input.money2').mff_mask('#.##0,00', { reverse: true });
('input.money3').mff_mask('#,##0.00', { reverse: true });
('input.money4').mff_mask('000,000,000,000,000.00', { reverse: true });
('input.money5').mff_mask('#.##0', { reverse: true });
('input.money6').mff_mask('#,##0', { reverse: true });
('input.ip_address').mff_mask('099.099.099.099');
('input.percent').mff_mask('##0,00%', { reverse: true });
('input.percent2').mff_mask('##0.00%', { reverse: true });
('input.percent3').mff_mask('990,0%', { reverse: true });
('input.percent4').mff_mask('990.0%', { reverse: true });
('input.percent5').mff_mask('#,##0%', { reverse: true });
('input.percent6').mff_mask('#.##0%', { reverse: true });
</code></pre>
<a href="https://gist.github.com/petermann/fd1a898e02ca91a0d7231a9f8ee662b4" rel="nofollow ugc">Click here</a> for more details on how to add custom mask.
Optional 
– Added option for the format of the Brazilian phone number, with attribute <code>name</code> equal to <code>phonebr</code>.
<h3>Credits</h3>
<a href="https://github.com/igorescobar/jQuery-Mask-Plugin" rel="nofollow ugc">jQuery Mask Plugin</a>

Masks Form Fields

A plugin to add masks in the form’s fields.

Placeholder Text vs Masks Form Fields