Urdu alphabet
Shahmukhi can be considered as a superset to Urdu alphabet because it has same alphabet as Urdu but with just 2 extra consonants; hence all Urdu readers can naturally read Shahmukhi (and vice-versa) without any practical difficulty. Urdu being the national language of Pakistan, Shahmukhi is colloquially just referred as Urdu script (or Urdu-Shahmukhi).