I have searched through the examples and the documentation (BTW the online document links are broken - the offline documentation is nice however).
/**< A tag for BLE stack configuration */
/// @param[in] conn_cfg_tag The connection to configure
ble_advertising_conn_cfg_tag_set(..., uint8_t ble_cfg_tag);
/// @param[in] ble_cfg_tag Configuration for the connection settings (see @ref ble_cfg_tag)
From what I infer, this value is associated with a BLE connection that can/may be established.
The idea is that in some future release of the SoftDevice you might use sd_ble_gap_adv_set_configure() to set a new advertising configuration and receive a handle for it. Currently (v6.0.0) the maximum number of advertising configurations is one, which means you only have the configuration with handle 1. (But you can change that configuration runtime if you want to.) The maximum number of advertising sets supported by the SoftDevice is found in BLE_GAP_ADV_SET_COUNT_MAX.
So it is a unique key for keeping track of an advertising configuration (not for keeping track of a connection.)
Thank you for the explanation!
I am using SDK 15 and MESH 2.0, and trying to merge the light switch demo with the ble_app_uart in folder ble_peripheral.
The problem is that I found the light switch demo will call sd_ble_gap_adv_set_configure() in mesh_adv.c while ble_app_uart also will use this function to get the advertising handle.(the updating of advertising handle will still cause a Mesh error 12292 at 0x00000000 (:0), which I don't have an ideal to debug it)
As you mentioned the maximum number of advertising handle is one for the softdevice v6.0.0. I wander if there is a way to control and pause the mash or the adv for ble_app_uart to let them work in different time intervals?