extensions/markdown-language-features/src/util/inMemoryDocument.ts/InMemoryDocument/lineAt
class InMemoryDocument:	lineAt(index: any): ITextLine {
		if (!this.lines) {
			this.lines = this._doc.getText().split(/\r?\n/).map(text => ({
				text,
				get isEmptyOrWhitespace() { return /^\s*$/.test(text); }
			}));
		}
		return this.lines[index];
	}