Bojjhanga: 'the 7 factors of enlightenment', are: awareness or mindfulness sati-sambojjhanga, sati, investigation of the law dhamma-vicaya-sambojjhanga energy viriya-sambojjhanga, viriya padhāna rapture pīti-sambojjhanga tranquillity passaddhi-sambojjhanga, concentration samādhi-sambojjhanga, equanimity upekkhā. Because they lead to enlightenment, therefore they are called factors of enlightenment see: XLVI, 5.
Though in the 2nd factor, dhamma-vicaya the word Dhamma is taken by most translators to stand for the Buddhist doctrine, it probably refers to the bodily and mental phenomena nāma-rūpa-dhammā as presented to the investigating mind by awareness or mindfulness, the 1st factor. With that interpretation, the term may be rendered by 'investigation of phenomena'.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.