In #974, it's been identified that new rules could really be helpful.

Especially:

• add a rule to ensure all variables used in server url are defined
• add a rule to ensure all defined server variables are used
• add a rule to ensure all parameters used in channel path are defined
• add a rule to ensure all defined channel parameters are used

The oas path-params custom function may be a great source of inspiration to fulfill that.

/cc @derberg