You can paste the placeholder rule outside the rule it is extracted, but I'd suggest before the first rule that uses it. You then put the rule want to use it like:
```scss
[href^='mailto:'] {
  @extend %grids-icon-button-padding-left-10-padding-right-10;
  // Other properties
}
```
You then use the same same `@extend` statement in the other rule below that is using the same rule.

PS: Sorry for the confusion I'll take a look at the Sass guide in the wiki to see what can be improved.