Original sentence: [1] 802.1Q has a 12-bit VLAN ID field, which has a theoretical limit of 2^12=4096.[2] The addition of a second tag allows operations that would not have been available had the VLAN id field simply been expanded from 12 bits to 24 bits (or any other large value).[3] A multi-tagged frame not only has multiple VLAN ID's, but has multiple EtherTypes and other VLAN header bit fields.[4] A tag stack creates a mechanism for Internet Service Providers to encapsulate customer single-tagged 802.1Q traffic with a single tag, the final frame being a QinQ frame.[5] QinQ frames are convenient means of constructing Layer 2 tunnels, or applying QoS policies, etc.[6] 802.1QinQ is upward compatible with 802.1Q.[7] It is easier for networking equipment makers to modify their existing equipment by creating multiple 802.1Q headers than to modify their equipment to implement some hypothetical new non-802.1Q extended VLAN-id field header
Edited sentence: 802.1Q has a 12-bit VLAN ID field, which has a theoretical limit of 2^12=4096.802.1QinQ is upward compatible with 802.1Q.A multi-tagged frame not only has multiple VLAN ID's, but has multiple EtherTypes and other VLAN header bit fields.A tag stack creates a mechanism for Internet Service Providers to encapsulate customer single-tagged 802.1Q traffic with a single tag, the final frame being a QinQ frame.It is easier for networking equipment makers to modify their existing equipment by creating multiple 802.1Q headers than to modify their equipment to implement some hypothetical new non-802.1Q extended VLAN-id field header.QinQ frames are convenient means of constructing Layer 2 tunnels, or applying QoS policies, etc.The addition of a second tag allows operations that would not have been available had the VLAN id field simply been expanded from 12 bits to 24 bits (or any other large value)