Preferred width of mrow-like elements

blah | 2

blah | 2

blah | 2

blah | 2

(blah | 2)

blah | 2

blah | 2

blah \frac{|_{3}}{4} 2

blah \frac{|_{3}}{4} 2

blah \frac{|_{3}}{4} 2

blah \frac{|_{3}}{4} 2

(blah, \frac{|_{3}}{4}, 2)

blah \frac{|_{3}}{4} 2

blah \frac{|_{3}}{4} 2