src/vs/editor/common/languages/supports/onEnter.ts/OnEnterSupport/_createOpenBracketRegExp
class OnEnterSupport:	private static _createOpenBracketRegExp(bracket: string): RegExp | null {
		let str = strings.escapeRegExpCharacters(bracket);
		if (!/\B/.test(str.charAt(0))) {
			str = '\\b' + str;
		}
		str += '\\s*$';
		return OnEnterSupport._safeRegExp(str);
	}