Having used Postscript for years, I am now learning SVG. There is a feature of PS that I have not been able to replicate so far: zero-width lines. In PS, a line with zero width is always visible: PostScript converts zero line width to the smallest printable width. On the screen, when zooming they never get any thinkness, yet are visible no matter the scale. I have used them when I wanted to render very thin lines, without worring about the final resolution I was going to use, and they turned out really useful.
However, in the official SVG docs (https://www.w3.org/TR/svg-strokes/) it says that:
A zero value causes no stroke to be painted. A negative value is invalid.
Is there a way in SVG to build zero-width lines in the sense of PostScript?
As Robert said, the nearest thing to what you want in SVG is vector-effect="non-scaling-stroke". This fixes the stroke width at 1 no matter how the SVG is scaled.
This works on Chrome and Firefox (and probably Opera - haven't checked), but AFAIK not IE/Edge.
<svg viewBox="0 0 100 100">
<rect x="10" y="10" width="80" height="80"
fill="none" stroke="black" stroke-width="1"
vector-effect="non-scaling-stroke"/>
</svg>Note that antialiasing will come into play depending on the position of the lines. The position will be affected by the scale.
If your lines are rectilinear (horizontal or vertical), you might also want to use shape-rendering="crispEdges". This will turn off antialiasing for the shape on which it is used, resulting in sharp one-pixel lines.
<svg viewBox="0 0 100 100">
<rect x="10" y="10" width="80" height="80"
fill="none" stroke="black" stroke-width="1"
vector-effect="non-scaling-stroke" shape-rendering="crispEdges"/>
</svg>