Halliday & Matthiessen (1999: 128-9):
Projecting sequences differentiate rather sharply between figures of sensing and saying, on the one hand, and figures of doing and being, on the other, by selecting figures of sensing and saying as the ones that have the special power of setting up other figures as second-order, semiotic reality. That is, projecting sequences construe figures of sensing and saying on two levels, the level of sensing/saying itself, and the level of the content of sensing/saying.