src/vs/editor/contrib/find/browser/findDecorations.ts/FindDecorations/getCurrentMatchesPosition
class FindDecorations:	public getCurrentMatchesPosition(desiredRange: Range): number {
		let candidates = this._editor.getModel().getDecorationsInRange(desiredRange);
		for (const candidate of candidates) {
			const candidateOpts = candidate.options;
			if (candidateOpts === FindDecorations._FIND_MATCH_DECORATION || candidateOpts === FindDecorations._CURRENT_FIND_MATCH_DECORATION) {
				return this._getDecorationIndex(candidate.id);
			}
		}
		// We don't know the current match position, so returns zero to show '?' in find widget
		return 0;
	}