extensions/markdown-language-features/src/preview/previewManager.ts/MarkdownPreviewManager/registerStaticPreview
class MarkdownPreviewManager:	private registerStaticPreview(preview: StaticMarkdownPreview): StaticMarkdownPreview {
		this._staticPreviews.add(preview);

		preview.onDispose(() => {
			this._staticPreviews.delete(preview);
		});

		this.trackActive(preview);
		return preview;
	}