AH Formatter / XSL Formatter
Q&A

FOは次のようになっていました。

<fo:flow>
  <fo:wrapper id="AAAAAA" />
  <fo:block space-before="2.0in">
  AAAAAAAA
  </fo:block>
</fo:flow>

fo:wrapper に id が指定されていると空の area が生成されます。したがってこのspace-beforeが指定されたブロックはページ先頭のエリアではないので、space-beforeは有効となります。

W3C XSL仕様1.1の6.13.4 fo:wrapperには以下のように記述されています。

Areas:
	
The fo:wrapper formatting object returns the sequence of areas created by concatenating 
the sequences of areas returned by each of the children of the fo:wrapper. If this sequence 
contains at least one normal area, or if the "id" and "index-key" properties are not specified 
on the fo:wrapper, then the fo:wrapper does not itself generate any areas.
	
If the sequence of areas returned to the fo:wrapper contains no normal areas, and the "id" or "index-key" 
property is specified on the fo:wrapper, then it additionally generates and returns one normal area 
with inline-progression-dimension and block-progression-dimension set to zero. This area is an 
inline-area except where this would violate the constraint (on some ancestor area) that an area's 
children are all block-areas or all inline-areas, but not a mixture. In that case the fo:wrapper must 
instead generate a block-area.	

fo:wrapperにidやindex-keyが指定された時は幅ゼロ/高さゼロの空エリアが生成されます。