ConnectionSubtype（连接子类型）
语义定义（Semantic definition）
物理端口连接子类型，进一步限定ConnectionType。推荐值如下：
- ACPLUG: A, B, C, D, E, F, EF, G, H, I, J, K, L, M
- DIN: Mini3P, Mini4P, Mini5P, Mini6P, Mini7P, Mini8P, Mini9P
- DSub: DA15, DB25, DC37, DD50, DE9, DE15
- EIAJ: RC5720
- HDMI: A, B, C
- RADIO: IEEE802.11g, IEEE802.11n
- RJ: 4P4C, 6P2C, 8P8C
- SOCKET: E-11, E-12, E-14, E-17, E-26, E-27, E-39, E-40
- TRS: TS_Mini, TS_SubMini, TRS_Mini, TRS_SubMini