What Is "leader" Formatting Object?

XSL-FO Tutorials - Herong's Tutorial Examples

∟What Is "leader" Formatting Object?

This section describes 'leader' formatting object, which is an inline-level formatting object that generates an inline area with flexible width with a repeating pattern to fill gaps between other inline areas.

What Is "leader" Formatting Object? "leader" is an inline-level formatting object that generates an inline area with flexible width with a repeating pattern to fill gaps between other inline areas.

Typical usages of "leader" formatting objects are:

To generate sequences of "." glyphs that separate titles from page numbers in table of contents.
To create entry fields in fill-in-the-blank forms.
To create horizontal rules for use as separators.

"leader" formatting objects support the following main attributes:

leader-pattern="..." - Optional attribute to specify the repeating pattern to be used to fill the gap. Supported values are: space - using space characters, rule - using a predefined rule style, dots - using dots, use-content - using specified content of the formatting object. Default is leader-pattern="space".
leader-length="..." - Optional attribute to specify the length of the repeating pattern. Supported values are: a specific length or a length range with 3 components: .length.minimum, .optimum, and .maximum. Default is (leader-length.minimum="0pt" leader-length.optimum="12pt" leader-length.maximum="100%")
rule-style="..." - Optional attribute to specify the rule style to be used for leader-pattern="rule". Supported values are none, dotted, dashed, solid, double, groove, and ridge. Default is rule-style="solid".
Other commonly used inline-level attributes.

If "leader" formatting object is used in block to generate a single line, you may want to use text-align-last="justify" to fill the full length of the line. Note that text-align="justify" does not apply to the last line of a paragraph. If a paragraph has only one line, it is considered as the last line.

To help understanding how to use "leader" formatting objects, I wrote this XSL-FO example, leader-Formatting-Object.fo:

<?xml version="1.0" encoding="utf-8"?>
<!-- leader-Formatting-Object.fo
 - Copyright (c) 2006 HerongYang.com. All Rights Reserved.
-->
<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
 <fo:layout-master-set>
  <fo:simple-page-master master-name="page" 
   margin="0.08in" page-height="3.3in" page-width="2.55in">
   <fo:region-body region-name="body" background-color="#eeeeee"/>
  </fo:simple-page-master>
 </fo:layout-master-set>
 <fo:page-sequence master-reference="page">
  <fo:flow flow-name="body">
   <fo:block margin="6pt" font-size="10pt" font-weight="bold"
    text-align="center">
Superman (1978)
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align="center">
Directed by Richard Donner
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" font-weight="bold"
    text-align="center">
Cast
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Marlon Brando <fo:leader leader-pattern="space"/> Jor-El
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Gene Hackman <fo:leader leader-pattern="dots"/> Lex Luthor
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Christopher Reeve <fo:leader leader-pattern="rule"/> Superman
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Christopher Reeve <fo:leader leader-pattern="rule" 
leader-length="20%"/> Superman
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Christopher Reeve <fo:leader leader-pattern="rule" 
leader-length.maximum="10%"/> Superman
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Christopher Reeve <fo:leader leader-pattern="rule" 
leader-length.maximum="0.2in"/> Superman
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Christopher Reeve <fo:leader leader-pattern="rule" 
leader-length="0.2in"/> Superman
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Ned Beatty <fo:leader leader-pattern="rule" rule-style="double"/> Otis
   </fo:block>
   <fo:block margin="6pt" font-size="8pt" text-align-last="justify">
Jackie Cooper <fo:leader leader-pattern="use-content">~</fo:leader> 
Perry White
   </fo:block>
   </fo:flow>
 </fo:page-sequence>
</fo:root>

If you process this example XSL-FO document with Apache FOP tool and view the output, you will see that the cast list of the Superman movie generated with different styles of "leader" formatting objects: