Is it permissible to declare a method with a name starting with a lowercase letter in an interface?

In Go (Golang), method names starting with a lowercase letter are considered unexported, meaning they are only accessible within the package where they are declared. You can declare methods with names starting with a lowercase letter in an interface, but then this interface will only be useful within the package, as such methods will not be visible outside.

If an interface is exported (starts with an uppercase letter), its methods are usually also exported (start with an uppercase letter) to be accessible outside the package.

Example:

package example

type MyInterface interface {
    doSomething() // method with a lowercase letter, unexported
}

Such an interface and its method are only accessible within the package example.

In summary: declaring methods with names starting with a lowercase letter in an interface is allowed, but it limits their visibility to the package.