<?php
// ...

public function getConfigTreeBuilder()
{
    $treeBuilder = new TreeBuilder();
    $rootNode = $treeBuilder->root('acme_title_case');
    // ...
}

InvalidArgumentException: There is no extension able to load the configuration for
"acme_titlecase" (in /Users/me/Sites/MySite/app/config/config.yml).
Looked for namespace "acme_titlecase",
found "framework", "another_namespace", ... , "acme_title_case", ...

<?php

namespace AcmeTitleCaseBundleDependencyInjection;

// ...

class AcmeTitleCaseExtension extends Extension
{
    // ...

    public function getAlias()
    {
        return 'acme_titlecase';
    }
}