this stuff about '''When you are walking along a path leading into a village, you can practice mindfulness. [...] You practice by keeping this one thought alive: "I'm walking along the path leading into the village"' ie
 "Furthermore, when walking, the monk discerns, 'I am walking.'
When standing, he discerns, 'I am standing.' When sitting, he
discerns, 'I am sitting.' When lying down, he discerns, 'I am lying
down.' Or however his body is disposed, that is how he discerns it.
"In this way he remains focused internally on the body in & of itself,
or focused externally... unsustained by anything in the world. This is
how a monk remains focused on the body in & of itself.
 "Furthermore, when going forward & returning, he makes himself
fully alert; when looking toward & looking away... when bending &
extending his limbs... when carrying his outer cloak, his upper robe &
his bowl... when eating, drinking, chewing, & savoring... when
urinating & defecating... when walking, standing, sitting, falling
asleep, waking up, talking, & remaining silent, he makes himself fully
is about a tiny part of mindfulness of the body, ie ''remaining focused on the body in & of itself'' (instead of caring about external objects) and being alert and so on.
You can go further with the parts of the body
Whether walking, standing, sitting, or lying down, it flexes &
stretches: this is the body's movement. Joined together with tendons &
bones, plastered over with muscle & skin, hidden by complexion, the
body isn't seen for what it is: filled with intestines, filled with
stomach, with the lump of the liver, bladder, lungs, heart, kidneys,
spleen, mucus, sweat, saliva, fat, blood, synovial fluid, bile, & oil.
On top of that, in nine streams, filth is always flowing from it: from
the eyes : eye secretions, from the ears : ear secretions, from the
nose : mucus, from the mouth : now vomit, now phlegm, now bile. from
the body : beads of sweat. And on top of that, its hollow head is
filled with brains.
Like MN10 mentions, there are plenty of other stuff to think about and do for ''remaining focused on the body in & of itself''
then there is also mindfulness of feelings-perceptions and dhammas.