For the Linux network engineering tool ebtables, I searched : "ebtables difference in using rule specification compared to match extension"

The response:
In ebtables, the main difference between using a rule specification and a match extension is that a rule specification represents a condition that determines which action to take, while a match extension allows users to activate Extend before sending the first message:

Rule specification
A rule specification is a condition used in a process to decide which action to take. Rule specifications are made up of command line arguments that are used in the add and delete commands. A "!" option before the specification inverts the test for that specification.

Match extension
A match extension allows users to activate Extend before sending the first message in all matches. In matches with women, non-binary people, and men, users can use Extend if the first move hasn't been made within the first 24 hours.