Discovered during Cisco CCNP course, Tcl (originally from “Tool Command Language“) is a scripting language created by John Ousterhout and introduced from IOS version 12.3(2)T.
But what is Cisco Tcl?
The Cisco IOS Tcl shell was designed to allow customers to run Tcl commands directly from the Cisco IOS CLI prompt. Cisco IOS software does contain some [...]

EtherChannel bundles individual Ethernet links into a single logical link that provides bandwidth up to 1600 Mbps (Fast EtherChannel, full duplex) or 16 Gbps (Gigabit EtherChannel) between two Cisco Catalyst switches. All interfaces in each EtherChannel must be the same speed and duplex, and both ends of the channel must be configured as either a [...]

As you see in the article “Implementing High Availability with HSRP“, it is quite simple configure Hot Standby Router Protocol.
Some cases require a custom configuration, using priority, track, preempt etc…and these are:

The standby preempt interface configuration command allows the router to become the active router when its priority is higher than all other HSRP-configured routers [...]