"Emacs can draw line-level indicators in the built-in fringe and margin, the thin gutters beside the buffer text. The fringe gives you a single monochrome mark per side, and the margin can technically hold more, but getting several independent sources to share one line cleanly is surprisingly hard to pull off in the plain text rendering that the margin uses out-of-the-box.

svg-margin (code on GitHub) fixes this by rendering indicators as SVG in the window margins, so any number of independent "providers" present text, icon glyphs, and clickable markers side by side on one line. Like my svg-line package, it overlays SVGs onto built-in UI components (the margin in this case) by leveraging Emacs's built-in SVG support. My personal config channels many sources to it, including VC, flycheck, evil marks, Org elements, whitespace indicators, and live symbol occurrences."