protected function scopedKey($node) {
    $attributes = $this->scopedAttributes($node);

    $output = array();

    foreach($attributes as $fld => $value)
      $output[] = $this->qualify($fld).'='.(is_null($value) ? 'NULL' : $value);

    // NOTE: Maybe an md5 or something would be better. Should be unique though.
    return implode(',', $output);
  }
protected function scopedKey($node) {
    $attributes = $this->scopedAttributes($node);

    $output = array();

    foreach($attributes as $fld => $value)
      $output[] = $this->qualify($fld).'='.(is_null($value) ? 'NULL' : $value);

    // NOTE: Maybe an md5 or something would be better. Should be unique though.
    return implode(',', $output);
  }
Return a string-key for the current scoped attributes. Used for index
computing when a scope is defined (acsts as an scope identifier).

@param   Baum\Node $node
@return  string