Neos\ContentRepository\Domain\Service\ContextFactory::mergeTargetDimensionContextProperties PHP Method

    protected function mergeTargetDimensionContextProperties(array $contextProperties, &$mergedProperties, $defaultContextProperties)
    {
        // Use first value of each dimension as default target dimension value
        $defaultContextProperties['targetDimensions'] = array_map(function ($values) {
            return reset($values);
        }, $mergedProperties['dimensions']);
        if (!isset($contextProperties['targetDimensions'])) {
            $contextProperties['targetDimensions'] = array();
        }
        $mergedProperties['targetDimensions'] = Arrays::arrayMergeRecursiveOverrule($defaultContextProperties['targetDimensions'], $contextProperties['targetDimensions']);
    }