Find open, closed and self-intersecting contours. Self-intersecting contours can be closed or open contours so you can select this option additionally!
Docs: https://y.stadtfabrikanten.org/contourscannerandtrimmer
TL;DR:
Bentley-Ottmann algorithm is used to check for those intersections. The algorithm works with the accuracy of the selected paths (epsilons). Self-intersections usually happen if you just have large overlaps where the contour crosses itself like an 'eight' character for example. Using the highlighting it's easy to find contours with unproper path handles. While in a CAD system an area of of a surface can only be calculated if the contour is closed and clean, finding self intersections in Inkscape is not required to do so. SVG format allows to calculate areas on open contours and self-twisted curves. This "artwork behaviour" makes it harder for handling machinery-like drawings for laser cutting, vinyl cutting or whatever. That's why we need to have extra sanity ch
