src/vs/editor/common/languages/supports/tokenization.ts/ThemeTrieElement/match
class ThemeTrieElement:	public match(token: string): ThemeTrieElementRule {
		if (token === '') {
			return this._mainRule;
		}

		const dotIndex = token.indexOf('.');
		let head: string;
		let tail: string;
		if (dotIndex === -1) {
			head = token;
			tail = '';
		} else {
			head = token.substring(0, dotIndex);
			tail = token.substring(dotIndex + 1);
		}

		const child = this._children.get(head);
		if (typeof child !== 'undefined') {
			return child.match(tail);
		}

		return this._mainRule;
	}