Here is a list of predefined validators. You cannot use these names for your custom validators.
<table width="500">
<tr>
    <td>
        <b>name</b>
    </td>
    <td>
        <b>arguments</b>
    </td>
    <td>
        <b>task</b>
    </td>
</tr>
<tr>
    <td>
        email
    </td>
    <td>

    </td>
    <td>
        Checks if value is valid email.
    </td>
</tr>
<tr>
    <td>
        notblank
    </td>
    <td>

    </td>
    <td>
        Checks if value is not blank.
    </td>
</tr>
<tr>
    <td>
        notnull
    </td>
    <td>

    </td>
    <td>
        Checks if value is not null.
    </td>
</tr>
<tr>
    <td>
        country
    </td>
    <td>

    </td>
    <td>
        Checks if value is valid country code.
    </td>
</tr>
<tr>
    <td>
        ip
    </td>
    <td>

    </td>
    <td>
        Checks if value is valid internet protocol address.
    </td>
</tr>
<tr>
    <td>
        htmlcolor
    </td>
    <td>

    </td>
    <td>
        Checks if value is valid html color.
    </td>
</tr>
<tr>
    <td>
        nospace
    </td>
    <td>

    </td>
    <td>
        Checks if value has no space chars.
    </td>
</tr>
<tr>
    <td>
        range
    </td>
    <td>
        [min, max]
    </td>
    <td>
        Checks if value is in range specified by arguments.
    </td>
</tr>
<tr>
    <td>
        unique
    </td>
    <td>

    </td>
    <td>
        Checks if value is unique in its database table.
    </td>
</tr>
<tr>
    <td>
        regexp
    </td>
    <td>
        [expression]
    </td>
    <td>
        Checks if value matches a given regexp.
    </td>
</tr>
</table>
