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.\" ========================================================================
.\"
.IX Title "Boulder::XML 3pm"
.TH Boulder::XML 3pm "2022-06-08" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Boulder::XML \- XML format input/output for Boulder streams
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&   use Boulder::XML;
\&   
\&   $stream = Boulder::XML\->newFh;
\&
\&   while ($stone = <$stream>) {
\&        print $stream $stone;
\&   }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Boulder::XML generates BoulderIO streams from \s-1XML\s0 files and/or
streams.  It is also able to output Boulder Stones in \s-1XML\s0 format.  Its
semantics are similar to those of Boulder::Stream, except that there
is never any pass-through behavior.
.PP
Because \s-1XML\s0 was not designed for streaming, some care must be taken
when reading an \s-1XML\s0 document into a series of Stones.  Consider this
\&\s-1XML\s0 document:
.PP
.Vb 1
\& <?xml version="1.0" standalone="yes"?>
\&
\& <Paper>
\&   <Author>Lincoln Stein</Author>
\&   <Author>Jean Siao</Author>
\&   <Date>September 29, 1999</Date>
\&   <Copyright copyrighted="yes">1999 Lincoln Stein</Copright>
\&   <Abstract>
\&       This is the abstract.  It is not anything very fancy,
\&       but it will do.
\&   </Abstract>
\&   <Citation>
\&        <Author>Fitchberg J</Author>
\&        <Journal>Journal of Irreproducible Results</Journal>
\&        <Volume>23</Volume>
\&        <Year>1998</Volume>
\&   </Citation>
\&   <Citation>
\&        <Author>Clemenson V</Author>
\&        <Journal>Ecumenica</Journal>
\&        <Volume>10</Volume>
\&        <Year>1968</Volume>
\&   </Citation>
\&   <Citation>
\&        <Author>Ruggles M</Author>
\&        <Journal>Journal of Aesthetic Surgery</Journal>
\&        <Volume>10</Volume>
\&        <Year>1999</Volume>
\&   </Citation>
\& </Paper>
.Ve
.PP
Ordinarily the document will be construed as a single Paper tag
containing subtags Author, Date, Copyright, Abstract, and so on.
However it might be desirable to fetch out just the citation tags as a
series of Stones.  In this case, you can declare Citation to be the
top level tag by passing the \fB\-tag\fR argument to \fBnew()\fR. Now calling
\&\fBget()\fR will return each of the three Citation sections in turn.  If no
tag is explicitly declared to be the top level tag, then Boulder::XML
will take the first tag it sees in the document.
.PP
It is possible to stream \s-1XML\s0 files.  You can either separate them into
separate documents and use the automatic \s-1ARGV\s0 processing features of
the BoulderIO library, or separate the \s-1XML\s0 documents using a
\&\fBdelimiter\fR string similar to the delimiters used in \s-1MIME\s0 multipart
documents.  By default, BoulderIO uses a delimiter of
<!\-\-Boulder::XML\-\->.
.PP
\&\fBThis is not a general \s-1XML\s0 parsing engine!\fR Instead, it is a way to
represent BoulderIO tag/value streams in \s-1XML\s0 format.  The module uses
XML::Parser to parse the \s-1XML\s0 streams, and therefore any syntactic
error in the stream can cause the \s-1XML\s0 parser to quit with an error.
Another thing to be aware of is that there are certain \s-1XML\s0
constructions that will not translate into BoulderIO format, specifically 
free text that contains embedded tags.  This is \s-1OK:\s0
.PP
.Vb 1
\&  <Author>Jean Siao</Author>
.Ve
.PP
but this is not:
.PP
.Vb 1
\&  <Author>The <Emphatic>extremely illustrious</Emphatic> Jean Siao</Author>
.Ve
.PP
In BoulderIO format, tags can contain other tags or text, but cannot
contain a mixture of tags and text.
.SS "\s-1CONSTRUCTORS\s0"
.IX Subsection "CONSTRUCTORS"
.ie n .IP "$stream = Boulder::XML\->new(*IN,*OUT);" 4
.el .IP "\f(CW$stream\fR = Boulder::XML\->new(*IN,*OUT);" 4
.IX Item "$stream = Boulder::XML->new(*IN,*OUT);"
.PD 0
.ie n .IP "$stream = Boulder::XML\->new(\-in=>*IN, \-out=>*OUT, \-tag=>$tag, \-delim=>$delim, \-strip=>$strip)" 4
.el .IP "\f(CW$stream\fR = Boulder::XML\->new(\-in=>*IN, \-out=>*OUT, \-tag=>$tag, \-delim=>$delim, \-strip=>$strip)" 4
.IX Item "$stream = Boulder::XML->new(-in=>*IN, -out=>*OUT, -tag=>$tag, -delim=>$delim, -strip=>$strip)"
.PD
\&\fBnew()\fR creates a new Boulder::XML stream that can be read from or
written to.  All arguments are optional.
.Sp
.Vb 3
\& \-in    Filehandle to read from. 
\&        If a file name is provided, will open the file.
\&        Defaults to the magic <> filehandle.
\&
\& \-out   Filehandle to write to.  
\&        If a file name is provided, will open the file for writing.
\&        Defaults to STDOUT
\&
\& \-tag   The top\-level XML tag to consider as the Stone record.  Defaults
\&        to the first tag seen when reading from an XML file, or to 
\&        E<lt>StoneE<gt> when writing to an output stream without
\&        previously having read.
\&
\& \-delim Delimiter to use for delimiting multiple Stone objects in an
\&        XML stream.
\&
\& \-strip If true, automatically strips leading and trailing whitespace 
\&        from text contained within tags.
.Ve
.ie n .IP "$fh = Boulder::XML\->newFh(*IN,*OUT);" 4
.el .IP "\f(CW$fh\fR = Boulder::XML\->newFh(*IN,*OUT);" 4
.IX Item "$fh = Boulder::XML->newFh(*IN,*OUT);"
.PD 0
.ie n .IP "$fh = Boulder::XML\->newFh(\-in=>*IN, \-out=>*OUT, \-tag=>$tag, \-delim=>$delim, \-strip=>$strip)" 4
.el .IP "\f(CW$fh\fR = Boulder::XML\->newFh(\-in=>*IN, \-out=>*OUT, \-tag=>$tag, \-delim=>$delim, \-strip=>$strip)" 4
.IX Item "$fh = Boulder::XML->newFh(-in=>*IN, -out=>*OUT, -tag=>$tag, -delim=>$delim, -strip=>$strip)"
.PD
The \fBnewFh()\fR constructor creates a tied filehandle that can read and
write Boulder::XML streams.  Invoking <> on the filehandle will
perform a \fBget()\fR, returning a Stone object.  Calling \fBprint()\fR on the
filehandle will perform a \fBput()\fR, writing a Stone object to output in
\&\s-1XML\s0 format.
.SS "\s-1METHODS\s0"
.IX Subsection "METHODS"
.ie n .IP "$stone = $stream\->\fBget()\fR" 4
.el .IP "\f(CW$stone\fR = \f(CW$stream\fR\->\fBget()\fR" 4
.IX Item "$stone = $stream->get()"
.PD 0
.ie n .IP "$stream\->put($stone)" 4
.el .IP "\f(CW$stream\fR\->put($stone)" 4
.IX Item "$stream->put($stone)"
.ie n .IP "$done = $stream\->done" 4
.el .IP "\f(CW$done\fR = \f(CW$stream\fR\->done" 4
.IX Item "$done = $stream->done"
.PD
All these methods have the same semantics as the similar methods in
Boulder::Stream, except that pass-through behavior doesn't apply.
.SH "AUTHOR"
.IX Header "AUTHOR"
Lincoln D. Stein <lstein@cshl.org>, Cold Spring Harbor Laboratory,
Cold Spring Harbor, \s-1NY.\s0  This module can be used and distributed on
the same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Boulder, Boulder::Stream, Stone