code: public static CharSequence drop(CharSequence self, int num) {
          if( num <= 0 ) {
              return self ;
          }
          if( self.length() <= num ) {
              return self.subSequence( 0, 0 ) ;
          }
          return self.subSequence(num, self.length()) ;
      }
docs: Drops the given number of chars from the head of this CharSequence
  if they are available.
  <pre class="groovyTestCase">
  def text = "Groovy"
  assert text.drop( 0 ) == 'Groovy'
  assert text.drop( 2 ) == 'oovy'
  assert text.drop( 7 ) == ''
  </pre>
  
  @param self the original CharSequence
  @param num the number of characters to drop from this iterator
  @return a CharSequence consisting of all characters except the first <code>num</code> ones,
  or else an empty String, if this CharSequence has less than <code>num</code> characters.
  @since 1.8.1