src/vs/platform/contextkey/common/contextkey.ts/ContextKeyRegexExpr/serialize
class ContextKeyRegexExpr:	public serialize(): string {
		const value = this.regexp
			? `/${this.regexp.source}/${this.regexp.ignoreCase ? 'i' : ''}`
			: '/invalid/';
		return `${this.key} =~ ${value}`;
	}