code: protected function buildHeader()
      {
          if ($this->getExtNamespace() === null) {
              throw new ExtDirectException("Ext js Namespace not set");
          }
  
          // Example: 'Ext.ns("Ext.app"); Ext.app.REMOTING_API = ';
          $var = 'Ext.ns("' . $this->getNameSpace() . '"); ' . $this->getNameSpace() . "." . Keys::EXT_HEADER . ' = ';
  
          return $var;
      }
docs: Builds ExtDirect Header
  
  @example Ext.ns('Ext.app'); Ext.app.REMOTING_API = {
  
  @return string
  @throws ExtDirectException