Tao-sheng: The Gāthās and the Prose

Thereupon Mañjuśrī, wishing to repeat what he had said, sang in gāthās in the midst of the great multitude:

As for the way the gāthās are composed, what was [mentioned] before [in prose] may sometimes be omitted and not chanted [in the gāthās]; what was not previously [in prose] may sometimes be included in the gāthās. It is also difficult to set a standard [on what is to be chanted]. It is possible only to determine provisionally at a specific point of time what should be [chanted].

Tao-sheng Commentary on the Lotus Sutra, p177