[1.6.x] Fixed typos in docs/ref/forms/validation.txt.

  ``ValidationError``.

* The ``validate()`` method on a Field handles field-specific validation

  that is not suitable for a validator, It takes a value that has been

  that is not suitable for a validator. It takes a value that has been

  coerced to correct datatype and raises ``ValidationError`` on any error.

  This method does not return anything and shouldn't alter the value. You

  should override it to handle validation logic that you can't or don't

Form field default cleaning

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let's firstly create a custom form field that validates its input is a string

Let's first create a custom form field that validates its input is a string

containing comma-separated email addresses. The full class looks like this::

    from django import forms