[1] XFA 2.4 939頁 (名無しさん [sage])

[2]

Vertical Alignment

A paragraph of text may be aligned vertically via the use of a text-valign style attribute which is a non-standard extension to [CSS2].

The supported alignments are limited to top, middle, and bottom.

Example:

<p style="text-valign:middle">
  This is the first line of the paragraph.<br />
  This is the second line of the paragraph.<br />
  This is the last line of the paragraph.<br />
</p>

(名無しさん [sage])