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Code Editor : dsssl2.htm

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<table border="0" width="780">
 <tr>
 <td valign="top"><img
 src="images/space.gif" alt="" width="145" height="10"></td>
 <td><h1>Experimental DSSSL extensions</h1>
 <h2>Contents</h2>
 <ul>
 <li><a href="#Introduction">Introduction</a> </li>
 <li><a href="#Imperative programming">Imperative programming</a> </li>
 <li><a href="#Style rules">Style
 rules</a> </li>
 <li><a href="#ExtendedPatterns">Extended
 Patterns</a> </li>
 <li><a href="#Multiple patterns per rule">Multiple patterns per rule</a> </li>
 <li><a href="#Flow object macros">Flow
 object macros</a> </li>
 <li><a href="#Characteristic value conversion">Characteristic value convertion</a> </li>
 <li><a href="#Characteristic names">Characteristic names</a> </li>
 </ul>
 <h2><a name="Introduction">Introduction</a></h2>
 This document descibes some
 experimental extensions to DSSSL that are implemented in OpenJade. 
	These are designed so that, with these extensions, DSSSL provides a 
 superset of the semantics <a
 href="http://www.w3.org/TR/NOTE-XSL-970910">XSL</a> for flow
 object tree construction. OpenJade has a <code>-2</code>
 option that enables these extensions. 
 These extensions do not include the
 additional flow object classes and characteristics that
 will be needed for XSL; in particular they do not include
 the HTML/CSS flow object classes. 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
 <h2><a name="Imperative programming">Imperative
 programming</a></h2>
 The following features come from R4RS:
 
 <ul>
 <li>assignment (<code>set!</code>)
 expressions (with <a href="#read-only">restrictions</a>) </li>
 <li>vectors (with <a
 href="#read-only">restrictions</a>) </li>
 <li><code>call-with-current-continuation</code>
 (with <a href="#call/cc">restrictions</a>) </li>
 <li><code>begin</code> expressions
 </li>
 <li>multiple expressions in
 procedure bodies, <code>cond</code> clauses </li>
 <li>alternate in <code>if</code>
 expression optional </li>
 <li>it is not an error when
 nothing matches in <code>cond</code> or <code>case</code>
 expression </li>
 <li><code>eqv?</code> and <code>memv</code>
 procedures; these behave as specified in R4RS for
 vectors but behave the same as <code>equal?</code>
 for strings and lists This is so that case expressions can
 use <code>eqv?</code> as required by R4RS without
 breaking compatibility with existing DSSSL code
 which assumes case expressions with strings and
 lists will use <code>equal?</code>. R4RS
 specifies that <code>eqv?</code> should return #t
 when its arguments &quot;should normally be
 regarded as the same object&quot;. R4RS treats
 strings and lists as mutable and its
 specification of <code>eqv?</code> for strings
 and lists is consistent with this. So long as
 DSSSL keeps strings and lists as immutable data-types
 with value semantics, it is more consistent to
 define <code>eqv?</code> to behave like <code>equal?</code>
 for them. 
 </li>
 </ul>
 The use of side-effects is
 restricted. Assignment to top-level variables is not
 allowed. There is also the concept that a memory location
 can be read-only. When a memory location is read-only, it
 is an error to change that location. An memory location
 can be recursively marked as read-only; this means that
 the memory location along with all memory locations
 reachable from that memory location become read-only. A
 memory location is recursively marked as read-only when: 
 <ul>
 <li>an object stored in that
 memory location is bound to a top-level variable </li>
 <li>an expression specifying a
 characteristic is evaluated and a variable that
 names that memory location occurs free in that
 expression; for example, this would be an error: <pre>
(let ((x 10pt))
 (make paragraph
 font-size: (begin (set! x 12pt) x)))
</pre>
 </li>
 <li>an object stored in that
 memory location is returned by a <code>(inherited-</code><code><var>C</var></code><code>)</code>
 or <code>(actual-</code><code><var>C</var></code><code>)</code>
 procedure </li>
 <li>an object stored in that
 memory location is passed as the first argument
 to the <code>node-list-map</code> procedure </li>
 </ul>
 A continuation created with <code>call-with-current-continuation</code>
 cannot be called if it is read-only, and can only be used
 to return to a stack frame in the current call chain (sometimes
 referred to as upwards only). 
 There's a <code>void</code> data
 type with a single value which can be written as <code>#v</code>.
 This is returned by <code>cond</code>, <code>case</code>
 and <code>if</code> expressions which don't match. 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
 <h2><a name="Style rules">Style rules</a></h2>
 When a construction rule has a
 keyword argument list instead of a construct expression
 it is treated as a style rule. For example, 
 <pre>
(element H1
 font-size: 14pt
 font-weight: 'bold)
</pre>
 The keyword argument list can
 include a <code>use:</code> keyword just as with <code>style</code>
 expressions. See the <a
 href="http://www.w3.org/TR/NOTE-XSL-970910">XSL proposal</a>
 for the semantics of style rules. 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
 <h2><a name="ExtendedPatterns">Extended
 patterns</a></h2>
 The syntax for element patterns is
 extended. These provide provide a superset of the
 semantics of XSL patterns. They are allowed both in
 element construction rules and in contexts where a <code>match-element?</code>
 pattern is currently allowed (eg <code>select-elements</code>,
 <code>process-matching-children</code>, <code>process-first-descendant</code>).
 
 A pattern is either a single gi or
 a list. A list consists of a sequence of gis, where each
 gi can be followed by one or more keyword/value pairs (where
 the value is always a single datum). A gi can be #t, a
 string or a symbol. The following keywords are allowed: 
 <dl>
 <dt><code>id:</code> </dt>
 <dd>followed by a string or symbol
 </dd>
 <dt><code>class:</code> </dt>
 <dd>followed by a string or symbol
 </dd>
 <dt><code>repeat:</code> </dt>
 <dd>followed by one of the symbols
 <code>*</code>, <code>+</code>, <code>?</code> </dd>
 <dt><code>only:</code> </dt>
 <dd>followed by one of the symbols
 <code>of-type</code>, <code>of-any</code> </dd>
 <dt><code>position:</code> </dt>
 <dd>followed by one of the symbols
 <code>first-of-type</code>, <code>first-of-any</code>,
 <code>last-of-type</code>, <code>last-of-any</code>
 </dd>
 <dt><code>attributes:</code> </dt>
 <dd>followed by a list of name/value
 pairs; for backward compatibility with <code>match-element?</code>
 patterns in the current DSSSL standard the <code>attributes:</code>
 keyword can be omitted; #t and #f can be used as
 a value to test for presence or absence of
 attributes. </dd>
 <dt><code>children:</code> </dt>
 <dd>followed by a pattern; each of
 the elements in the pattern must occur as child; <code>repeat:</code>
 is not allowed in children patterns; the <code>children:</code>
 qualifier is allowed on any gi in a pattern not
 just the last element </dd>
 <dt><code>priority:</code> </dt>
 <dd>followed by an integer;
 multiple <code>priority:</code> qualifiers are
 allowed in a pattern and will be added together </dd>
 <dt><code>importance:</code> </dt>
 <dd>followed by an integer;
 multiple <code>importance:</code> qualifiers are
 allowed and will be added together </dd>
 </dl>
 Class attribute names are declared
 using 
 <pre>
(declare-class-attribute &quot;<var>class</var>&quot;)
</pre>
 or 
 <pre>
(declare-class-attribute <var>class</var>)
</pre>
 Id attribute names can be declared
 similarily using <code>declare-id-attribute</code>. 
 Some examples: 
 <pre>
(element (E importance: 42) <var>...</var>)

(element (E attributes: (A1 V1)) <var>...</var>)

(element (P E children: C) <var>...</var>)

(element (P children: C priority: -11
 E children: C attributes: (A1 V1 A2 V2))
 <var>...</var>)

(element (P E children: (A children: C B children: C)) <var>...</var>)
</pre>
 The last is equivalent to the
 following in XSL syntax: 
 <pre>
&lt;element type=&quot;P&quot;&gt;
 &lt;target-element type=&quot;E&quot;&gt;
 &lt;element type=&quot;A&quot;&gt;
 &lt;element type=&quot;C&quot;/&gt;
 &lt;/element&gt;
 &lt;element type=&quot;B&quot;&gt;
 &lt;element type=&quot;C&quot;/&gt;
 &lt;/element&gt;
 &lt;/target-element&gt;
&lt;/element&gt;
</pre>
 <pre><a href="#top"><img
src="images/top-of-page.gif" alt="Up" border="0" width="11"
height="15"></a><a href="#top">Back to top</a>&nbsp;</pre>
 <h2><a name="Multiple patterns per rule">Multiple patterns per rule</a></h2>
 An <code>or-element</code>
 construction rule has the syntax 
 <pre>
(or-element (<var>pattern</var>+) <var>expression</var>)
</pre>
 where <code><var>pattern</var></code>
 is any pattern that could be allowed in an element
 construction rule. It is equivalent to a sequence of
 element construction rules. 
 For example, 
 <pre>
(or-element (H1 H2 H3)
 font-weight: 'bold)

(or-element ((H1 TITLE) (H2 TITLE) (H3 TITLE))
 font-weight: 'bold)
</pre>
 is equivalent to 
 <pre>
(element H1
 font-weight: 'bold)

(element H2
  font-weight: 'bold)

(element H3
  font-weight: 'bold)

(element (H1 TITLE)
  font-weight: 'bold)

(element (H2 TITLE)
  font-weight: 'bold)

(element (H3 TITLE)
 font-weight: 'bold)
</pre>
 <pre><a href="#top"><img
src="images/top-of-page.gif" alt="Up" border="0" width="11"
height="15"></a><a href="#top">Back to top</a>&nbsp;</pre>
 <h2><a name="Flow object macros">Flow
 object macros</a></h2>
 A flow object macro can be defined
 like this: 
 &nbsp; 
 <div align="left"><table border="0" width="546"
 bgcolor="#FFFFBB">
 <tr>
 <td width="542"><dl>
 <dt>(declare-flow-object-macro
 list-item ((indent 1in) (marker &quot;\bullet&quot;)
 #!contents contents) 
 &nbsp; (make paragraph 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 first-line-start-indent: (- indent) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 start-indent: (+ indent (inherited-start-indent)) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (make
 line-field 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 field-width: indent 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal marker)</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 ) 
 &nbsp; contents</dt>
 <dt>&nbsp; )</dt>
 <dt>) 
 
 (root 
 &nbsp;&nbsp;&nbsp; (make simple-page-sequence 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make paragraph 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Para 1&quot;)</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 ) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make list-item 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Item 1&quot;) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make list-item 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 indent: .5in 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 marker: &quot;\black-circle&quot; 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Sub item 1.1&quot;)</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 )</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 ) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make list-item 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 font-weight: 'bold 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Item 2&quot;) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make list-item 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Sub item 2.1&quot;)</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 )</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 ) 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (make paragraph 
 &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 (literal &quot;Para 2&quot;)</dt>
 <dt>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 )</dt>
 <dt>&nbsp;&nbsp;&nbsp; )</dt>
 <dt>)</dt>
 </dl>
 </td>
 </tr>
 </table>
 </div>If the formal argument list
 includes <code>#!contents</code> the flow object behaves
 like a compound flow object, otherwise like an atomic
 flow object. Inherited characteristics can be specified;
 these are applied to a sequence flow object which is
 automatically wrapped around what is returned by the body
 of the flow object macro. The preceding formal arguments
 are the non-inherited characteristics; like keyword
 arguments they can be specified either as <code><var>id</var></code>
 (in which case they default to #f), or as <code>(</code><code><var>id</var></code><code>
 </code><code><var>init-expression</var></code><code>)</code>.
 
 Note that flow object macros are
 quite different from ordinary procedures in that the
 macro body is not evaluated when the make expression is
 evaluated, but rather when the flow object is to be added
 to the tree; this allows <code>(inherited-</code><code><var>c</var></code><code>)</code>
 and <code>(actual-</code><code><var>c</var></code><code>)</code>
 procedures to be used in flow object macro
 characteristics, non-inherited as well as inherited, just
 as with normal flow objects. It is also possible to use <code>(inherited-</code><code><var>c</var></code><code>)</code>
 and <code>(actual-</code><code><var>c</var></code><code>)</code>
 procedures in the body of the flow object macro; they
 will return the same result as if they were used in the
 specification of a characteristic on the invocation of
 the flow object macro. 
 For an example of a library built
 with the macro facility read: <a
 href="../DSSSL/HTML%20Sample.html">Simple
 XML to HTML Conversion and Rendition Example</a> 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
 <h2><a name="Characteristic value conversion">Characteristic value conversion</a></h2>
 Most characteristic values can now
 be specified as strings and will be converted
 appropriately. For boolean valued characteristics any of
 the strings <code>&quot;true&quot;</code>, <code>&quot;false&quot;</code>,
 <code>&quot;yes&quot;</code> and <code>&quot;no&quot;</code>
 are acceptable. 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
 <h2><a name="Characteristic names">Characteristic
 names</a></h2>
 The question mark that can be
 omitted from those DSSSL characteristic names that end
 with a question mark. This is because the question mark
 is not (and cannot reasonably be made) a legal XML name
 character. 
 <a href="#top"><img
 src="images/top-of-page.gif" alt="Up" border="0"
 width="11" height="15"></a><a href="#top">Back to top</a>&nbsp; 
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