# $Id$
#
# >>Copyright::
# Copyright (c) 1992-1996, Ian Clatworthy (ianc@mincom.com).
# You may distribute under the terms specified in the LICENSE file.
#
# >>History::
# -----------------------------------------------------------------------
# Date      Who     Change
# 29-Feb-96 ianc    SDF 2.000
# -----------------------------------------------------------------------
#

H1: Filters

H2: Introduction

A {{filter}} controls how a block of text is interpreted.
The text is usually delimited by {{MAC:block}} and {{MAC:endblock}}
macros.

For example, tables are usually defined via the {{FILT:table}} filter:

E:!block table
E:Option  Description
E:-h      display help
E:-o      specify the output extension
E:!endblock

The result is:

!block table
Option  Description
-h      display help
-o      specify the output extension
!endblock


H2: Commonly used filters

Some of the commonly used filters are:

!block table; coltags='FILT'
Filter      Description
table       the lines are a table in SDF's {{FMT:TBL}} format
example     the lines are example paragraphs
title       used to build a title block for memos, faxes, etc.
topics      include files as sub-topics
appendix    replace H1 styles with A1, etc.
plain       replace H1 styles with P1, etc.
!endblock

A complete list of the supported filters and their parameters
is given in the {{DOC: SDF Reference}} manual.


H2: Other macros supporting filters

Other macros also support filters. These include:

* {{MAC:include}} - include text from another file
* {{MAC:execute}} - include the output of a system command.

For example, the following line includes another [[SDF]] file
and formats it as an appendix:

E:   !include "tips.sdf"; appendix

Note: The {{FILT:appendix}} and {{FILT:plain}} filters enable
authors to construct topics without needing to worry about how
those topics will be used, e.g. a topic may be a chapter in
one document and an appendix in another!