On our map, we need to mark polygons, points and lines. The TEI <zone> element is officially defined as marking an area:

"defines any two-dimensional area within a surface element"

which is arguably a polygon only. I've been dealing with points by creating tiny one-pixel zones using the old attributes designed for rectangles (@ulx, @uly, @lrx, @lry), but we've been rather abusing the @points attribute intended for polygons to handle lines (paths), with a convention that if a list of points does not repeat its initial point, it's not closed, and is therefore a path. I tried to get that officially sanctioned and change the definition of <zone> and @points, but was not successful (https://sourceforge.net/p/tei/feature-requests/541/), and they've asked me to prepare a feature request for a <path> element instead, which I fear will not be successful (the feeling is that this crosses too far into SVG territory).

So we are now officially engaged in some mild tag-abuse. The suggested fix was that instead of a series of coordinates creating a line, we should have a one-pixel-wide shape instead; that would be functionally identical to a line, but would really be a zone and would therefore be OK. So I'm now providing this in the XML we serve up (the "Standard" and "Standalone" variants) by expanding the attributes on the fly, so that we're providing good TEI to anyone who wants it, but we're not making our lives needlessly complicated for the sake of purity.