What is doctrine on ordinary daily posture?

In this question I'm asking about posture -- holding the body straight, for example -- not especially asking about posture *during formal meditation*, which was the topic of previous questions. --- I was surprised to read [this answer](https://buddhism.stackexchange.com/a/24013/254) , which includes, > ... walking straight, aware of body posture, like a king/queen, straight, not like a cowboy or a pig, awareness of the body and correct it. Sometimes (though, not often) I see something similar in other answers, [for example](https://buddhism.stackexchange.com/a/14092/254) : > You need to develop a good posture, good grace, and good gait. You should sit, stand, and walk conveniently, with good energy flow. I was surprised to see that because: - I don't remember that's being a doctrine in the suttas -- at most maybe I remember comments on (or descriptions of) the Buddha's or Rahula's physical appearance, e.g. "like a lion" etc. - Buddhist doctrine emphasises view, and knowledge, and wisdom and so on -- if there is a mind-versus-body dichotomy, I'd expect Buddhism is more on the "mind" side of things. - Some doctrines seem intended to deemphasise the value of the body -- meditations on the foulness of the body, contemplation of corpses, etc. --- So -- *what* is doctrine about posture (from suttas, from what you've been taught, and/or from your personal experience)? And, do you know, *why*? And what is *difficult* about that practice? And does that affect your *social* relationships, somehow? How does it interact with practicing prostration?