<milestone> marks a boundary point separating any kind of section of a text, as indicated by
changes in a standard reference system, where the section is not
represented by a structural element. 3.10.3 Milestone
Elements
If the milestone marks the beginning of a piece of text not
present in the reference edition, the special value absent
may be used as the value of unit. The normal interpretation
is that the reference edition does not contain the text which follows,
until the next milestone tag for the edition in question is
encountered.
In addition to the values suggested, other terms may be appropriate
(e.g. Stephanus for the Stephanus numbers in Plato).
For this element, the global n attribute indicates the new number or other value for the unit which changes
at this milestone. The special value unnumbered should be used in
passages which fall outside the normal numbering scheme (e.g. chapter
heads, poem numbers or titles, or speaker attributions in verse
drama).
The order in which milestone elements are given at a given point is not normally
significant.