197 lines
7.7 KiB
TeX
197 lines
7.7 KiB
TeX
\section{Standard Module \sectcode{sgmllib}}
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\label{module-sgmllib}
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\stmodindex{sgmllib}
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\index{SGML}
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This module defines a class \code{SGMLParser} which serves as the
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basis for parsing text files formatted in SGML (Standard Generalized
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Mark-up Language). In fact, it does not provide a full SGML parser
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--- it only parses SGML insofar as it is used by HTML, and the module
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only exists as a base for the \code{htmllib} module.
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\refstmodindex{htmllib}
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In particular, the parser is hardcoded to recognize the following
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constructs:
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\begin{itemize}
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\item
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Opening and closing tags of the form
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\samp{<\var{tag} \var{attr}="\var{value}" ...>} and
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\samp{</\var{tag}>}, respectively.
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\item
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Numeric character references of the form \samp{\&\#\var{name};}.
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\item
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Entity references of the form \samp{\&\var{name};}.
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\item
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SGML comments of the form \samp{<!--\var{text}-->}. Note that
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spaces, tabs, and newlines are allowed between the trailing
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\samp{>} and the immediately preceeding \samp{--}.
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\end{itemize}
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The \code{SGMLParser} class must be instantiated without arguments.
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It has the following interface methods:
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\setindexsubitem{(SGMLParser method)}
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\begin{funcdesc}{reset}{}
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Reset the instance. Loses all unprocessed data. This is called
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implicitly at instantiation time.
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\end{funcdesc}
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\begin{funcdesc}{setnomoretags}{}
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Stop processing tags. Treat all following input as literal input
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(CDATA). (This is only provided so the HTML tag \code{<PLAINTEXT>}
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can be implemented.)
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\end{funcdesc}
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\begin{funcdesc}{setliteral}{}
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Enter literal mode (CDATA mode).
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\end{funcdesc}
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\begin{funcdesc}{feed}{data}
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Feed some text to the parser. It is processed insofar as it consists
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of complete elements; incomplete data is buffered until more data is
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fed or \code{close()} is called.
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\end{funcdesc}
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\begin{funcdesc}{close}{}
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Force processing of all buffered data as if it were followed by an
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end-of-file mark. This method may be redefined by a derived class to
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define additional processing at the end of the input, but the
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redefined version should always call \code{SGMLParser.close()}.
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\end{funcdesc}
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\begin{funcdesc}{handle_starttag}{tag\, method\, attributes}
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This method is called to handle start tags for which either a
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\code{start_\var{tag}()} or \code{do_\var{tag}()} method has been
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defined. The \code{tag} argument is the name of the tag converted to
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lower case, and the \code{method} argument is the bound method which
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should be used to support semantic interpretation of the start tag.
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The \var{attributes} argument is a list of (\var{name}, \var{value})
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pairs containing the attributes found inside the tag's \code{<>}
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brackets. The \var{name} has been translated to lower case and double
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quotes and backslashes in the \var{value} have been interpreted. For
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instance, for the tag \code{<A HREF="http://www.cwi.nl/">}, this
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method would be called as \code{unknown_starttag('a', [('href',
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'http://www.cwi.nl/')])}. The base implementation simply calls
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\code{method} with \code{attributes} as the only argument.
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\end{funcdesc}
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\begin{funcdesc}{handle_endtag}{tag\, method}
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This method is called to handle endtags for which an
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\code{end_\var{tag}()} method has been defined. The \code{tag}
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argument is the name of the tag converted to lower case, and the
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\code{method} argument is the bound method which should be used to
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support semantic interpretation of the end tag. If no
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\code{end_\var{tag}()} method is defined for the closing element, this
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handler is not called. The base implementation simply calls
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\code{method}.
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\end{funcdesc}
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\begin{funcdesc}{handle_data}{data}
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This method is called to process arbitrary data. It is intended to be
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overridden by a derived class; the base class implementation does
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nothing.
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\end{funcdesc}
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\begin{funcdesc}{handle_charref}{ref}
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This method is called to process a character reference of the form
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\samp{\&\#\var{ref};}. In the base implementation, \var{ref} must
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be a decimal number in the
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range 0-255. It translates the character to \ASCII{} and calls the
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method \code{handle_data()} with the character as argument. If
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\var{ref} is invalid or out of range, the method
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\code{unknown_charref(\var{ref})} is called to handle the error. A
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subclass must override this method to provide support for named
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character entities.
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\end{funcdesc}
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\begin{funcdesc}{handle_entityref}{ref}
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This method is called to process a general entity reference of the form
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\samp{\&\var{ref};} where \var{ref} is an general entity
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reference. It looks for \var{ref} in the instance (or class)
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variable \code{entitydefs} which should be a mapping from entity names
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to corresponding translations.
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If a translation is found, it calls the method \code{handle_data()}
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with the translation; otherwise, it calls the method
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\code{unknown_entityref(\var{ref})}. The default \code{entitydefs}
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defines translations for \code{\&}, \code{\&apos}, \code{\>},
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\code{\<}, and \code{\"}.
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\end{funcdesc}
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\begin{funcdesc}{handle_comment}{comment}
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This method is called when a comment is encountered. The
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\code{comment} argument is a string containing the text between the
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\samp{<!--} and \samp{-->} delimiters, but not the delimiters
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themselves. For example, the comment \samp{<!--text-->} will
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cause this method to be called with the argument \code{'text'}. The
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default method does nothing.
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\end{funcdesc}
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\begin{funcdesc}{report_unbalanced}{tag}
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This method is called when an end tag is found which does not
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correspond to any open element.
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\end{funcdesc}
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\begin{funcdesc}{unknown_starttag}{tag\, attributes}
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This method is called to process an unknown start tag. It is intended
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to be overridden by a derived class; the base class implementation
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does nothing.
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\end{funcdesc}
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\begin{funcdesc}{unknown_endtag}{tag}
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This method is called to process an unknown end tag. It is intended
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to be overridden by a derived class; the base class implementation
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does nothing.
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\end{funcdesc}
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\begin{funcdesc}{unknown_charref}{ref}
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This method is called to process unresolvable numeric character
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references. It is intended to be overridden by a derived class; the
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base class implementation does nothing.
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\end{funcdesc}
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\begin{funcdesc}{unknown_entityref}{ref}
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This method is called to process an unknown entity reference. It is
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intended to be overridden by a derived class; the base class
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implementation does nothing.
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\end{funcdesc}
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Apart from overriding or extending the methods listed above, derived
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classes may also define methods of the following form to define
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processing of specific tags. Tag names in the input stream are case
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independent; the \var{tag} occurring in method names must be in lower
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case:
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\begin{funcdescni}{start_\var{tag}}{attributes}
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This method is called to process an opening tag \var{tag}. It has
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preference over \code{do_\var{tag}()}. The \var{attributes} argument
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has the same meaning as described for \code{handle_starttag()} above.
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\end{funcdescni}
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\begin{funcdescni}{do_\var{tag}}{attributes}
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This method is called to process an opening tag \var{tag} that does
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not come with a matching closing tag. The \var{attributes} argument
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has the same meaning as described for \code{handle_starttag()} above.
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\end{funcdescni}
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\begin{funcdescni}{end_\var{tag}}{}
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This method is called to process a closing tag \var{tag}.
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\end{funcdescni}
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Note that the parser maintains a stack of open elements for which no
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end tag has been found yet. Only tags processed by
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\code{start_\var{tag}()} are pushed on this stack. Definition of an
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\code{end_\var{tag}()} method is optional for these tags. For tags
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processed by \code{do_\var{tag}()} or by \code{unknown_tag()}, no
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\code{end_\var{tag}()} method must be defined; if defined, it will not
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be used. If both \code{start_\var{tag}()} and \code{do_\var{tag}()}
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methods exist for a tag, the \code{start_\var{tag}()} method takes
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precedence.
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