Here was an bug in "_require.php". It included file that needed the interface before the interface itself.

FluentDOM/FluentDOM@93db8d4

FluentDOM uses this file, if it the classes/interfaces are not loaded.

The selectors will be more complex. If the Symfony library is installed and available you can copy the src/Transformer.php somewhere and register an callback that provides it:

FluentDOM::registerXpathTransformer(
  function() {
    require_once(__DIR__.'/Transformer.php');
    return new \FluentDOM\Symfony\CssSelector\Transformer;
  }
);

Composer

Composer does several things for you. It installs packages including their dependencies. For example if you install fluentdom/selectors-symfony it will install fluentdom\fluentdom and symfony/css-selector, too. It handles versions, too.

The second part is the autoloader. Composer includes an autoloader that is configured by the composer.json files. You only need to require vendor/autoload.php and all classes/inerfaces from the installed packages will be available.

from fluentdom.

Ok !
I finally managed to make it with composer. Thanks for the explanations.
So I used

$ composer require fluentdom/selectors-symfony --ignore-platform-reqs

Now the libraries are loaded, but it throws an error :

require_once($this->plugin_dir . '_inc/php/autoload.php');

Fatal error: Call to undefined method FluentDOM::registerXpathTransformer() in .../_inc/php/fluentdom/selectors-symfony/src/plugin.php on line 5

It seems that composer doesn't load the correct version, is it it ?
Because if I replace the fluentdom/fluentdom folder with the files from github, it seems to work.

[EDIT]
Ok, I updated my php server, it now works !
It was just difficult to know giving the previous error...

from fluentdom.

If you download the files from GitHub, you will fetch "master". This is the current development version (5.3dev). Composer will install 5.2 stable by default. One of the differences is the CSS selector integration. In 5.2 is is a part of the FluentDOM core, so you do not need fluentdom/selectors-symfony. 5.3 has got the registration and separate integration packages.

from fluentdom.