For everyone getting this warning from W3C validator: "Text run is not in Unicode Normalization Form C."
See:
http://www.w3.org/International/docs/charmod-norm/#choice-of-normalization-form
Requires PHP 5.3+
Be sure to have the PHP-Normalizer-extension (intl and icu) installed.
See:
http://php.net/manual/en/normalizer.normalize.php
See also:
https://core.trac.wordpress.org/ticket/30130