in reply to Re: XML round-trip with comments and
in thread XML round-trip with comments and prolog

At first, I thought that might get too low-level for me. But then I saw that XML::Rules->new has a handlers => {...} which allows defining handlers for XML::Parser::Expat events. Some experimentation with a dummy callback to handle them all says that Comment and XMLDecl are the events I want during the parsing.

#!perl use 5.012; # strict, // use warnings; use Data::Dump; use XML::Rules; my $xml_doc = <<EOXML; <?xml version="1.0" encoding="UTF-8" ?> <!-- important instructions to manual editors --> <root> <group name="blah"> <!-- important instructions for group "blah" --> <tag/> </group> <group name="second"> <!-- important instructions for group "second" --> <differentTag/> </group> </root> EOXML my $callback = sub { my ($name, $parser, @args) = @_; print STDERR "event:", $name//'<undef>', "("; print STDERR join ', ', map {defined($_) ? qq("$_") : '<undef>'} @ +args; print STDERR ")\n"; }; my %handlers = (); for my $h ( qw/Comment XMLDecl/ ) { #qw/Start End Char Proc Comment Cd +ataStart CdataEnd Default Unparsed Notation ExternEnt ExternEntFin En +tity Element Attlist Doctype DoctypeFin XMLDecl/) { $handlers{$h} = sub { $callback->($h => @_) } } my $parser = XML::Rules->new( stripspaces => 3|4, rules => [ _default => 'raw', ], handlers => \%handlers, ); #dd my $data = $parser->parse($xml_doc); print my $out = $parser->ToXML($data, 0, " ", "") . "\n"; __DATA__ event:XMLDecl("1.0", "UTF-8", <undef>) event:Comment(" important instructions to manual editors ") event:Comment(" important instructions for group "blah" ") event:Comment(" important instructions for group "second" ") <root> <group name="blah"> <tag/> </group> <group name="second"> <differentTag/> </group> </root>

Now that I've got that far, I should be able to get the prolog and comments into the data object (by returning values, instead of just printing messages). But the harder part will be how to get ->ToXML() to do something on the output. I may have to subclass XML::Rules to get additional outputs for my comment and prolog data items -- if anyone has an easier idea than that, feel free to let me know.

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Re^3: XML round-trip with comments and
by pryrt (Monsignor) on Jul 28, 2021 at 19:13 UTC
    I should be able to get the prolog and comments into the data object

    I was optimistic. I misunderstood that the handler return expectations would match the rule return expectations, and whatever was returned from the handler would be added to the data structure, similarly to a custom rule. That didn't happen. And with haukex's advice that round-tripping is difficult, this might not be the right path after all. If anyone has advice for continuing down this path, I will definitely experiment with it, no matter which direction I go from here.