How access array with specials characters in array key

I suggest using a custom ViewHelper. One example is kind of just copy paste + adjusting the namespace, from powermail: https://github.com/einpraegsam/powermail/blob/develop/Classes/ViewHelpers/Misc/VariableInVariableViewHelper.php

<?php
declare(strict_types=1);
namespace In2code\Powermail\ViewHelpers\Misc;

use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Extbase\Reflection\Exception\PropertyNotAccessibleException;
use TYPO3\CMS\Extbase\Reflection\ObjectAccess;
use TYPO3Fluid\Fluid\Core\ViewHelper\AbstractViewHelper;
use TYPO3Fluid\Fluid\Core\Rendering\RenderingContextInterface;
use TYPO3Fluid\Fluid\Core\ViewHelper\Traits\CompileWithRenderStatic;
use TYPO3Fluid\Fluid\Core\ViewHelper\ViewHelperInterface;

/**
 * Class VariableInVariableViewHelper
 */
class VariableInVariableViewHelper extends AbstractViewHelper implements ViewHelperInterface
{
    use CompileWithRenderStatic;

    /**
     * Initialize arguments.
     */
    public function initializeArguments()
    {
        parent::initializeArguments();
        $this->registerArgument('obj', 'mixed', 'Object', true);
        $this->registerArgument('prop', 'string', 'Property', true);
    }

    /**
     * Solution for {outer.{inner}} call in fluid
     *
     * @param array $arguments
     * @param \Closure $renderChildrenClosure
     * @param RenderingContextInterface $renderingContext
     *
     * @return mixed
     * @throws PropertyNotAccessibleException
     */
    public static function renderStatic(
        array $arguments,
        \Closure $renderChildrenClosure,
        RenderingContextInterface $renderingContext
    ) {
        $obj = $arguments['obj'];
        $prop = $arguments['prop'];
        if (is_array($obj) && array_key_exists($prop, $obj)) {
            return $obj[$prop];
        }
        if (is_object($obj)) {
            return ObjectAccess::getProperty($obj, GeneralUtility::underscoredToLowerCamelCase($prop));
        }
        return null;
    }
}

Another option would be to prepare your data in the controller to a more "suitable" format.

In your question, you hide the most important thing - the key value. However as we can see it's a URL with a domain name it's quite obvious it contains a dot inside, which is the problem.

Literally, the Fluid tries to access the array structure like it was nested one level deeper, so instead of

$array['http://example.com/path/to/your/script'] it tries to access
$array['http://example']['com/path/to/your/script'].

You don't mention what is the clue of using such complicated keys for your array, anyway you need to get rid of the special chars to make it work.

One way is converting that structure in your controller, before assigning to the view. It's a simple foreach(), so I won't write it, but you need to get a structure like (pseudo code)

$array = [
    'xml_base' => '',
    'children' => [
        'http_domain_com_path_to_your_script' = [
             'url' => 'http://example.com/path/to/your/script',
             'other' => 'attr',
        ],
        'http_another_com_path_to_your_script' = [
             'url' => 'http://another.com/path/to/your/script',
             'other' => 'attr',
        ],
    ]
]

and access it as parent.children.http_domain_com_path_to_your_script

or even convert it to the non-associative array

$array = [
    'xml_base' => '',
    'children' => [
        [
            'url' => 'http://example.com/path/to/your/script',
            'other' => 'attr',
        ],
        [
            'url' => 'http://another.com/path/to/your/script'
            'other' => 'attr',
        ],
    ]
]

So you can access it by numeric values like parent.children.0

Finally, you can also check Georg's solution, which allows accessing such keys, anyway didn't test ever, and personally I prefer way with simplified keys.

Georg Ringer's suggestion got me on the right track. I added a custom Viewhelper to to acccess the custom rss tags via SimplePIE. It takes the namespace and that tag I need and return the desired values.

Thank you all very much for your help.