With the exception of one word, this preamble is self-explanatory. The one word is parimukham, translated here as “to the fore.” The Abhidhamma, when commenting on this passage, gives an etymological interpretation of this word, saying that parimukha means “around the mouth” (pari = around;mukha = mouth or face). In other words, when focused on the breath, you should focus on the area around the mouth. However, the Vinaya (Cv.V.27.4) contains a prohibition against dressing the hair of the parimukha. Because the same passage also contains a separate prohibition against dressing the beard around the mouth as a goatee, the Commentary interprets parimukha in this case as meaning “on the chest.” Obviously, then, the word has several meanings, and the question is whether it should be understood literally as meaning a particular section of the body, or more idiomatically as bringing something to the forefront. Evidence for this latter interpretation comes from passages in the Canon where monks focusing on topics of meditation aside from the breath are nevertheless described as having established mindfulness parimukham.For example, in Ud 7:8, Ven. MahaKaccayana establishes mindfulness parimukham when engaged in mindfulness immersed in the body; in MN 62, Ven. Rahula establishes mindfulness parimukham when contemplating the theme of not-self with regard to the five aggregates. Because it makes no sense to say that a person contemplating either of these topics should focus awareness exclusively on one part of the body to the exclusion of others—and because, in step 3 of the first tetrad in breath meditation, the awareness will become whole-body anyway—it makes more sense to interpret the phrase, “mindfulness established parimukhaª” as an idiom for bringing mindfulness to the fore. In other words, you bring the topic you plan to keep in mind up to the forefront of your awareness.
(Thanissaro, Right Mindfulness, p. 88-9)
Here the term parimukham is one of those simple words that is so hard to interpret. It literally means 'around the mouth'. It is interpreted by the Vibhanga as 'at the nose top', while modern renderings usually use something vague like 'in front'. However the phrase frequently occurs in contexts outside of anapanasati, making the interpenetration 'at the nose-tip', or any literal spatial interpretation, unlikely. The Sanskrit has a different reading, pratimukha.256 This has many meanings, among which are 'reflection' and 'presence'. Both of these would be appropriate in meditative context. But the word usually, as here, occurs in close conjunction with upatthana, which also means 'presence'. I think we have another example of that common feature of Pali or Sanskrit, a conjunction of synonyms for emphasis: literally, 'one makes present a presence of presence of mind', or more happily, one establishes presence of mindfulness.'
(Sujato, A History of Mindfulness, p. 108-9)
Both the Abhidhamma and the commentaries take "in front" (parimukham) to indicate a precise anatomical location.46 In the discourses, however, the specification "In front" occurs in a variety of contexts, such as for example, in relation to overcoming the hindrances or to developing the divine abodes (brahmavihara).47 Although overcoming the hindrances can occur with the aid of mindfulness of breathing, this is not necessarily the case. In fact, the standard instructions for overcoming the hindrances do not mention the breath.48 Similary, the discourses do not relate the development of the divine abodes in any way to awarenss of the breath.49. Apart from awareness of the breath, however, to direct mindfulness to the nostril area makes little sense, whether in relation to overcoming the hindrances or to developing the divine abodes. Thus, at least in these contexts, the figurative sense of "in front" as a first establishment of sati is the more meaningful alternative.
Therefore, although to understand "in front" to indicate the nostril area makes sense in relation to mindfulness of breathing, alternative ways of practice, based on a more figurative understanding of the term, cannot be categorically excluded. In fact, several modern teachers have developed successful approaches to mindfulness of breathing independent of the nostril area. Some, for example, advice their pupils to experience the breath in the chest area, others suggest observing the air element at the abdomen, while still others recommend directing awareness to the act of breathing itself, without focusing on any specific location.50
(Analayo, Satipatthana, p. 124-5).
So satova assasati, satova passasati.
One mindfully inhales, mindfully exhales.
I suppose "always" is Thanssiaro's addition, driving a point about continuity of mindfulness.
Analayo notes that according to Chit Tin "this instruction refers in particular to clearly distinguishing between the in-breath and the out-breath"
Because steps 1 and 2 are not described as “trainings,” we can infer that in the beginning stages of familiarizing yourself with the breath you don’t consciously try to adjust it. You simply try to discern variations in the breath. The same principle would appear to apply to questions of whether the breath is fast or slow, shallow or deep, heavy or light.
(Thanissaro, Right Mindfulness, p. 89)
Another interpenetration is that long breath is an earlier stage, and the short breath represents greater calm. The progression from knowing longer breaths to knowing shorter breaths reflects the fact that the breath naturally becomes shorter and finer with continued contemplation, owing to increasing mental and physical calmness.52
You see the joys of figuring out a dead language?