The optional argument inner-pos controls the placement of content inside the parbox.
Its default is the value of position.
Its possible values are: t to put the content at the top of the box, c to put it in the vertical center, b to put it at the bottom of the box, and s to stretch it out vertically (for this, the text must contain vertically stretchable space).
我觉得这段话的描述应该是准确的。
问 parbox的外部位置为c的排版效果与书上描述的不同