how to validate letters and whitespaces using Zend Framework ?
i think Zend_Validate_Regex is best for this situation
The Zend Framework does have a Zend_Validate_Alpha (as well as an alphanumeric version).
Normally it doesn't allow white space, but if you pass a true into the constructor of the Zend_Validate_Alpha class it will allow whitespace. Same with Zend_Validate_Alnum.
For example:
$validator = new Zend_Validate_Alpha(true); //will allow whitespace and non number letters