title: Use a regular expression to validate string
body: <p>I want to use regular expression to validate in input value wich is a string
  could contain upper and lower case , could have blank spaces and it's length could be between 0 and 255 caracter (0 :user could not give a value the field is nullable)</p>
  
  <p>I have using the folowing expression but it didn't work</p>
  
  <pre><code>/**
       * @var string
       *
       *  @Assert\Regex(
       *     pattern="/[a-zA-Z]{0,255}/",
       *     match=true,
       *     message="NameProj Invalid")
       *
       * @ORM\Column(name="NameProj ", type="string", length=255, nullable=true)
       */
      private $NameProj ;
  </code></pre>