\[ x + x + x + x + x + x + x + x + x + x + x + x \tag{a long tag} \] \[ x+ x + x + x + x\tag{a long tag} \] \[ x+ x + x + x + x\tag{x} \] \[ x+ x + x + x + x\\\Rule{1px}{.5em}{0px} \]