When an object is placed on a page, it can be positioned absolute or relative. Most objects are relative, which means that if the preceding objects grow/become larger, that the relative objects will shift (in most languages it shifts down).

 

We have seen that XSL-FO documents have flow layout, that is, the content flows from one page to the next one, according to the rules imposed by page breaks, spacing, widows and orphans properties. However, sometimes it may be useful to position elements at absolute coordinates.

 

Only fo:block-container can be placed absolutely, and this can be done by setting the position property to 'absolute' or 'fixed'.

 

The value 'fixed' means that the object has a position relative to the page.

The value 'absolute' means that the object has a position relative to the containing reference-area, typically another fo:block-container. This containing reference-area does not need to be positioned absolutely, which means you can position an object on a specific absolute location relative to another object that flows in the page.

 

In the example below, we have two fragments of text positioned under and over the main flow text:

 

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">

 <fo:layout-master-set>

       <fo:simple-page-master master-name="p1" page-width="7in"

                                                       page-height="2in">

               <fo:region-body region-name="xsl-region-body"

                                                       margin="0.2in"/>

       </fo:simple-page-master>

       <fo:simple-page-master master-name="p2" page-width="7in"

                                                       page-height="2in">

               <fo:region-body region-name="xsl-region-body" margin="0.2in"

                                                       column-count="2"/>

       </fo:simple-page-master>

       <fo:page-sequence-master master-name="default-sequence">

               <fo:single-page-master-reference master-reference="p1"/>

               <fo:repeatable-page-master-reference master-reference="p2"/>

       </fo:page-sequence-master>

 </fo:layout-master-set>

 <fo:page-sequence master-reference="default-sequence">

       <fo:flow flow-name="xsl-region-body" font-family="Verdana"

                                                               font-size="10pt">

               <fo:block-container position="absolute" top="10pt" left="30pt"

                                                       height="14pt" width="100%"> (1)

                       <fo:block font="72pt Arial" color="silver">Under</fo:block>

               </fo:block-container>

               <fo:block>

                       <fo:block>

                               Text Text Text Text Text Text Text Text Text Text        

                               .................................................                                            

                               Text Text Text Text Text Text Text Text Text Text        

                       </fo:block>

                       <fo:block-container position="absolute" top="20pt" left="40pt"

                                                               height="14pt" width="100%">

                               <fo:block font="72pt Arial" color="red">Over</fo:block>

                       </fo:block-container>

               </fo:block>

               <fo:block break-before="page"/>

               <fo:block-container position="absolute" top="10pt" left="30pt"

                                                        height="14pt" width="100%">

                       <fo:block font="72pt Arial" color="silver">Under</fo:block>

               </fo:block-container>

               <fo:block>

                       <fo:block>

                               Text Text Text Text Text Text Text Text Text Text        

                               ..................................................        

                               Text Text Text Text Text Text Text Text Text Text        

                       </fo:block>

                       <fo:block-container position="absolute" top="10pt" left="30pt"

                                                               height="14pt" width="100%">

                               <fo:block font="72pt Arial" color="red">Over</fo:block>

                       </fo:block-container>

               </fo:block>

       </fo:flow>

  </fo:page-sequence>

</fo:root>

 

The rendering result is displayed in the next figure:

 

 Figure 15.

 

The important point in this document is:

(1) position attribute is set to absolute ; top, bottom, left and right coordinates also are specified explicitly.

 

To change the order in which the elements are rendered, use z-index attribute:

 

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">

       <fo:layout-master-set>

               <fo:simple-page-master master-name="p1" page-width="7in"

                                                               page-height="2in">

                       <fo:region-body region-name="xsl-region-body"

                                                               margin="0.2in"/>

               </fo:simple-page-master>

       </fo:layout-master-set>

       <fo:page-sequence master-reference="p1">

               <fo:flow flow-name="xsl-region-body" font-family="Verdana"

                                                               font-size="12pt">

                       <fo:block>

                               Before Before Before Before Before Before        

                               ..........................................        

                               Before Before Before Before Before Before        

                       </fo:block>

                       <fo:block-container z-index="-1" position="absolute"

                                                               top="38pt" left="0pt">

                               <fo:block font="48pt Arial" color="rgb(192,192,192)"

                                               text-align="center">Under</fo:block>

                       </fo:block-container>

                       <fo:block-container z-index="+1" position="absolute"

                                                               top="48pt" left="10pt">

                               <fo:block font="48pt Arial" color="red"

                                                       text-align="center">Over</fo:block>

                       </fo:block-container>

                       <fo:block>

                               After After After After After After After After After        

                               .....................................................                

                               After After After After After After After After After        

                       </fo:block>

               </fo:flow>

       </fo:page-sequence>

</fo:root>

 

 Figure 16.

All elements are considered to have a z-index of 0, therefore, if you want an element to be displayed on the background (like a watermark) use a negative z-index, while for a foreground element (like a stamp) use a positive z-index.