This rule applies whenever an @if directive is followed by one or more @else if directives; the final @else if directive should be followed by an @else directive.

The requirement for a final @else directive is defensive programming.

The @else directive should either take appropriate action or contain a suitable comment as to why no action is taken.

Noncompliant Code Example

@if $x == 0 {
  do-something();
} @else if $x == 1 {
  do-something-else();
}

Compliant Solution

@if $x == 0 {
  do-something();
} @else if $x == 1 {
  do-something-else();
} @else {
  @error "Unexpected value for $x: #{$x}";
}