Visuddhimagga VIII-230

Apicettha pītipade pītisīsena vedanā vuttā.

然而于此（第二四法）中，于（五）「喜」之句是以喜的首目而说（相应）受的，

Ñ(VIII,230): Here, moreover, in the 'happiness' clause feeling [which is actually being contemplated in this tetrad] is stated under the heading of 'happiness' [which is a formation]

Sukhapade sarūpeneva vedanā.

于（六）「乐」之句是依自性受说，

Ñ: but in the 'bliss' clause feeling is stated in its own form.

Dvīsu cittasaṅkhārapadesu ‘‘saññā ca vedanā ca cetasikā ete dhammā cittapaṭibaddhā cittasaṅkhārā’’ti (paṭi. ma. 1.174; ma. ni. 1.463) vacanato saññāsampayuttā vedanāti evaṃ vedanānupassanānayena idaṃ catukkaṃ bhāsitanti veditabbaṃ.

于（七）（八）二「心行」之句即「想与受心所。此（二）法与心连结，为心行」之语，故「想」为相应受。[PTS 289] 如是当知是依（四念处中第二的）受随观（念处）的方法而说此（第二）四法。

Ñ: In the two 'mental-formation' clauses the feeling is that [necessarily] associated with perception because of the words, 'Perception and feeling belong to the mind, these things being bound up with the mind are mental formations' (Ps.i,188). [289]

So this tetrad should be understood to deal with contemplation of feeling.