code: public function getVersion()
      {
          if ($this->_version === null) {
              $this->_version = $this->defaultVersion();
          } else {
              if (!is_scalar($this->_version)) {
                  $this->_version = call_user_func($this->_version, $this);
              }
          }
  
          return $this->_version;
      }
docs: Returns current module version.
  If version is not explicitly set, [[defaultVersion()]] method will be used to determine its value.
  @return string the version of this module.
  @since 2.0.11