PdfHighlight
One entry of PdfViewState.highlights: where to paint (hit) plus how to paint it.
KiteSearchHit stays a pure text-search result, with no idea colours exist; this wraps one with the viewer's paint choices. Build the hit yourself from quads you already hold, or take it straight out of PdfDocument.search / KiteStructuredText.search.
Parameters
the page index and the display-space quads to cover.
fill for those quads. Null (the default) paints PdfViewColors.searchHighlight, exactly what PdfViewState.searchHighlights does, so wrapping a plain hit changes nothing on screen.
also paint a small rounded marker in one page margin, level with this highlight. It tells a reader a note lives on this page without them having to find the highlighted words. Every dimension is a fraction of the rendered page width, so it keeps its proportions in a thumbnail and at deep zoom alike, and its inner edge is clamped past the highlighted quads so it never paints over the words. On a page whose text reaches into that margin, leaving no room, nothing is drawn.
fill for that marker. Null (the default) falls back to color, and then to PdfViewColors.searchHighlight. A marker usually wants a stronger, opaque colour than the translucent fill next to it.
which margin carries the marker. PdfMarkerSide.End is the pre-0.5.1 behaviour and stays the default.