code: private function parseUnionMemberTypes()
      {
          $types = [];
          if ($this->skip(Token::EQUALS)) {
              // Optional leading pipe
              $this->skip(Token::PIPE);
              do {
                  $types[] = $this->parseNamedType();
              } while ($this->skip(Token::PIPE));
          }
  
          return $types;
      }
docs: UnionMemberTypes :
  - = `|`? NamedType
  - UnionMemberTypes | NamedType
  
  @return NamedTypeNode[]