src/vs/editor/common/languages/supports/onEnter.ts/OnEnterSupport/_createCloseBracketRegExp
class OnEnterSupport:	private static _createCloseBracketRegExp(bracket: string): RegExp | null {
		let str = strings.escapeRegExpCharacters(bracket);
		if (!/\B/.test(str.charAt(str.length - 1))) {
			str = str + '\\b';
		}
		str = '^\\s*' + str;
		return OnEnterSupport._safeRegExp(str);
	}