extensions/ipynb/src/notebookAttachmentCleaner.ts/AttachmentCleaner/saveAttachmentToCache
class AttachmentCleaner:	private saveAttachmentToCache(notebookUri: string, cellFragment: string, currFilename: string, metadata: { [key: string]: any }): void {
		const documentCache = this._attachmentCache.get(notebookUri);
		if (!documentCache) {
			// no cache for this notebook yet
			const cellCache = new Map<string, IAttachmentData>();
			cellCache.set(currFilename, this.getMetadataAttachment(metadata, currFilename));
			const documentCache = new Map();
			documentCache.set(cellFragment, cellCache);
			this._attachmentCache.set(notebookUri, documentCache);
		} else if (!documentCache.has(cellFragment)) {
			// no cache for this cell yet
			const cellCache = new Map<string, IAttachmentData>();
			cellCache.set(currFilename, this.getMetadataAttachment(metadata, currFilename));
			documentCache.set(cellFragment, cellCache);
		} else {
			// cache for this cell already exists
			// add to cell cache
			documentCache.get(cellFragment)?.set(currFilename, this.getMetadataAttachment(metadata, currFilename));
		}
	}