وَالْعَامِلُ فِيهِمَا مَعْنَوِيٌّ، وَهُوَ الِابْتِدَاءُ.
Translation: Their governor is non-overt and conceptual, namely ibtidāʾ (initiation of the nominal predication).
The author calls this a maʿnawī ʿāmil rather than an overt word such as إِنَّ or a preposition. This presents the textbook’s traditional analysis; grammatical schools explain governance in more than one way.