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authorPeter Bernard West <pbwest@apache.org>2003-03-06 09:11:57 +0000
committerPeter Bernard West <pbwest@apache.org>2003-03-06 09:11:57 +0000
commitdecc4a93de20170e558673b5013078abb75280a1 (patch)
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-<?xml version="1.0" standalone="no"?>
-<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN"
- "http://cvs.apache.org/viewcvs.cgi/*checkout*/xml-forrest/src/resources/schema/dtd/document-v11.dtd">
-
-<document>
- <header>
- <title>Property Expression Parsing</title>
- <authors>
- <person id="pbw" name="Peter B. West" email="pbwest@powerup.com.au"/>
- </authors>
- </header>
- <body>
- <section>
- <title>Property expression parsing</title>
- <note>
- The following discussion of the experiments with alternate
- property expression parsing is very much a work in progress,
- and subject to sudden changes.
- </note>
- <p>
- The parsing of property value expressions is handled by two
- closely related classes: <code>PropertyTokenizer</code> and its
- subclass, <code>PropertyParser</code>.
- <code>PropertyTokenizer</code>, as the name suggests, handles
- the tokenizing of the expression, handing <em>tokens</em>
- back to its subclass,
- <code>PropertyParser</code>. <code>PropertyParser</code>, in
- turn, returns a <code>PropertyValueList</code>, a list of
- <code>PropertyValue</code>s.
- </p>
- <p>
- The tokenizer and parser rely in turn on the datatype
- definition from the <code>org.apache.fop.datatypes</code>
- package and the datatype <code>static final int</code>
- constants from <code>PropertyConsts</code>.
- </p>
- <section>
- <title>Data types</title>
- <p>
- The data types currently defined in
- <code>org.apache.fop.datatypes</code> include:
- </p>
- <table>
- <tr><th colspan="2">Numbers and lengths</th></tr>
- <tr>
- <th>Numeric</th>
- <td colspan="3">
- The fundamental numeric data type. <em>Numerics</em> of
- various types are constructed by the classes listed
- below.
- </td>
- </tr>
- <tr>
- <td/>
- <th colspan="3">Constructor classes for <em>Numeric</em></th>
- </tr>
- <tr>
- <td/><td>Angle</td>
- <td colspan="2">In degrees(deg), gradients(grad) or
- radians(rad)</td>
- </tr>
- <tr>
- <td/><td>Ems</td>
- <td colspan="2">Relative length in <em>ems</em></td>
- </tr>
- <tr>
- <td/><td>Frequency</td>
- <td colspan="2">In hertz(Hz) or kilohertz(kHz)</td>
- </tr>
- <tr>
- <td/><td>IntegerType</td><td/>
- </tr>
- <tr>
- <td/><td>Length</td>
- <td colspan="2">In centimetres(cm), millimetres(mm),
- inches(in), points(pt), picas(pc) or pixels(px)</td>
- </tr>
- <tr>
- <td/><td>Percentage</td><td/>
- </tr>
- <tr>
- <td/><td>Time</td>
- <td>In seconds(s) or milliseconds(ms)</td>
- </tr>
- <tr><th colspan="2">Strings</th></tr>
- <tr>
- <th>StringType</th>
- <td colspan="3">
- Base class for data types which result in a <em>String</em>.
- </td>
- </tr>
- <tr>
- <td/><th>Literal</th>
- <td colspan="2">
- A subclass of <em>StringType</em> for literals which
- exceed the constraints of an <em>NCName</em>.
- </td>
- </tr>
- <tr>
- <td/><th>MimeType</th>
- <td colspan="2">
- A subclass of <em>StringType</em> for literals which
- represent a mime type.
- </td>
- </tr>
- <tr>
- <td/><th>UriType</th>
- <td colspan="2">
- A subclass of <em>StringType</em> for literals which
- represent a URI, as specified by the argument to
- <em>url()</em>.
- </td>
- </tr>
- <tr>
- <td/><th>NCName</th>
- <td colspan="2">
- A subclass of <em>StringType</em> for literals which
- meet the constraints of an <em>NCName</em>.
- </td>
- </tr>
- <tr>
- <td/><td/><th>Country</th>
- <td>An RFC 3066/ISO 3166 country code.</td>
- </tr>
- <tr>
- <td/><td/><th>Language</th>
- <td>An RFC 3066/ISO 639 language code.</td>
- </tr>
- <tr>
- <td/><td/><th>Script</th>
- <td>An ISO 15924 script code.</td>
- </tr>
- <tr><th colspan="2">Enumerated types</th></tr>
- <tr>
- <th>EnumType</th>
- <td colspan="3">
- An integer representing one of the tokens in a set of
- enumeration values.
- </td>
- </tr>
- <tr>
- <td/><th>MappedEnumType</th>
- <td colspan="2">
- A subclass of <em>EnumType</em>. Maintains a
- <em>String</em> with the value to which the associated
- "raw" enumeration token maps. E.g., the
- <em>font-size</em> enumeration value "medium" maps to
- the <em>String</em> "12pt".
- </td>
- </tr>
- <tr><th colspan="2">Colors</th></tr>
- <tr>
- <th>ColorType</th>
- <td colspan="3">
- Maintains a four-element array of float, derived from
- the name of a standard colour, the name returned by a
- call to <em>system-color()</em>, or an RGB
- specification.
- </td>
- </tr>
- <tr><th colspan="2">Fonts</th></tr>
- <tr>
- <th>FontFamilySet</th>
- <td colspan="3">
- Maintains an array of <em>String</em>s containing a
- prioritized list of possibly generic font family names.
- </td>
- </tr>
- <tr><th colspan="2">Pseudo-types</th></tr>
- <tr>
- <td colspan="4">
- A variety of pseudo-types have been defined as
- convenience types for frequently appearing enumeration
- token values, or for other special purposes.
- </td>
- </tr>
- <tr>
- <th>Inherit</th>
- <td colspan="3">
- For values of <em>inherit</em>.
- </td>
- </tr>
- <tr>
- <th>Auto</th>
- <td colspan="3">
- For values of <em>auto</em>.
- </td>
- </tr>
- <tr>
- <th>None</th>
- <td colspan="3">
- For values of <em>none</em>.
- </td>
- </tr>
- <tr>
- <th>Bool</th>
- <td colspan="3">
- For values of <em>true/false</em>.
- </td>
- </tr>
- <tr>
- <th>FromNearestSpecified</th>
- <td colspan="3">
- Created to ensure that, when associated with
- a shorthand, the <em>from-nearest-specified-value()</em>
- core function is the sole component of the expression.
- </td>
- </tr>
- <tr>
- <th>FromParent</th>
- <td colspan="3">
- Created to ensure that, when associated with
- a shorthand, the <em>from-parent()</em>
- core function is the sole component of the expression.
- </td>
- </tr>
- </table>
- </section>
- <section>
- <title>Tokenizer</title>
- <p>
- The tokenizer returns one of the following token
- values:
- </p>
- <source>
- static final int
- EOF = 0
- ,NCNAME = 1
- ,MULTIPLY = 2
- ,LPAR = 3
- ,RPAR = 4
- ,LITERAL = 5
- ,FUNCTION_LPAR = 6
- ,PLUS = 7
- ,MINUS = 8
- ,MOD = 9
- ,DIV = 10
- ,COMMA = 11
- ,PERCENT = 12
- ,COLORSPEC = 13
- ,FLOAT = 14
- ,INTEGER = 15
- ,ABSOLUTE_LENGTH = 16
- ,RELATIVE_LENGTH = 17
- ,TIME = 18
- ,FREQ = 19
- ,ANGLE = 20
- ,INHERIT = 21
- ,AUTO = 22
- ,NONE = 23
- ,BOOL = 24
- ,URI = 25
- ,MIMETYPE = 26
- // NO_UNIT is a transient token for internal use only. It is
- // never set as the end result of parsing a token.
- ,NO_UNIT = 27
- ;
- </source>
- <p>
- Most of these tokens are self-explanatory, but a few need
- further comment.
- </p>
- <dl>
- <dt>AUTO</dt>
- <dd>
- Because of its frequency of occurrence, and the fact that
- it is always the <em>initial value</em> for any property
- which supports it, AUTO has been promoted into a
- pseudo-type with its on datatype class. Therefore, it is
- also reported as a token.
- </dd>
- <dt>NONE</dt>
- <dd>
- Similarly to AUTO, NONE has been promoted to a pseudo-type
- because of its frequency.
- </dd>
- <dt>BOOL</dt>
- <dd>
- There is a <em>de facto</em> boolean type buried in the
- enumeration types for many of the properties. It had been
- specified as a type in its own right in this code.
- </dd>
- <dt>MIMETYPE</dt>
- <dd>
- The property <code>content-type</code> introduces this
- complication. It can have two values of the form
- <strong>content-type:</strong><em>mime-type</em>
- (e.g. <code>content-type="content-type:xml/svg"</code>) or
- <strong>namespace-prefix:</strong><em>prefix</em>
- (e.g. <code>content-type="namespace-prefix:svg"</code>). The
- experimental code reduces these options to the payload
- in each case: an <code>NCName</code> in the case of a
- namespace prefix, and a MIMETYPE in the case of a
- content-type specification. <code>NCName</code>s cannot
- contain a "/".
- </dd>
- </dl>
- </section>
- <section>
- <title>Parser</title>
- <p>
- The parser retuns a <code>PropertyValueList</code>,
- necessary because of the possibility that a list of
- <code>PropertyValue</code> elements may be returned from the
- expressions of soem properties.
- </p>
- <p>
- <code>PropertyValueList</code>s may contain
- <code>PropertyValue</code>s or other
- <code>PropertyValueList</code>s. This latter provision is
- necessitated for the peculiar case of of
- <em>text-shadow</em>, which may contain whitespace separated
- sublists of either two or three elements, separated from one
- another by commas. To accommodate this peculiarity, comma
- separated elements are added to the top-level list, while
- whitespace separated values are always collected into
- sublists to be added to the top-level list.
- </p>
- <p>
- Other special cases include the processing of the core
- functions <code>from-parent()</code> and
- <code>from-nearest-specified-value()</code> when these
- function calls are assigned to a shorthand property, or used
- with a shorthand property name as an argument. In these
- cases, the function call must be the sole component of the
- expression. The pseudo-element classes
- <code>FromParent</code> and
- <code>FromNearestSpecified</code> are generated in these
- circumstances so that an exception will be thrown if they
- are involved in expression evaluation with other
- components. (See Rec. Section 5.10.4 Property Value
- Functions.)
- </p>
- <p>
- The experimental code is a simple extension of the existing
- parser code, which itself borrowed heavily from James
- Clark's XT processor.
- </p>
- </section>
- </section>
- </body>
-</document>
-
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