The "kitchen sink" module for manipulating XML is XML::Twig.

A starting point using XML::Twig to solve you problem may be:

use strict;
use warnings;
use XML::Twig;

my $xml = <<XML;
<xs:complexType name="semt.002.001.01">
<xs:sequence>
<xs:element name="PrvsRef" type="AdditionalReference2" minOccurs="0" m
+axOccurs="unbounded"/>
<xs:element name="RltdRef" type="AdditionalReference2" minOccurs="0" m
+axOccurs="unbounded"/>
<xs:element name="MsgPgntn" type="Pagination"/>
<xs:element name="StmtGnlDtls" type="Statement3"/>
<xs:element name="AcctDtls" type="SafekeepingAccount1"/>
<xs:element name="BalForAcct" type="AggregateBalanceInformation1" minO
+ccurs="0" maxOccurs="unbounded"/>
<xs:element name="SubAcctDtls" type="SubAccountIdentification1" minOcc
+urs="0" maxOccurs="unbounded"/>
<xs:element name="TtlVals" type="TotalValueInPageAndStatement" minOccu
+rs="0" maxOccurs="1"/>
<xs:element name="Xtnsn" type="Extension1" minOccurs="0" maxOccurs="un
+bounded"/>
</xs:sequence>
</xs:complexType>
XML

my $twig = XML::Twig->new (twig_handlers => {'[@name]' => \&showNestin
+g});

$twig->parse ($xml);


sub showNesting {
    my @path;

    for my $elt (reverse $_->ancestors_or_self ()) {
        next unless defined $elt->att ('name');

        push @path, $elt->att ('name');
    }

    print join ('.', @path), "\n" if @path;
}
[download]

Prints:

semt.002.001.01.PrvsRef
semt.002.001.01.RltdRef
semt.002.001.01.MsgPgntn
semt.002.001.01.StmtGnlDtls
semt.002.001.01.AcctDtls
semt.002.001.01.BalForAcct
semt.002.001.01.SubAcctDtls
semt.002.001.01.TtlVals
semt.002.001.01.Xtnsn
semt.002.001.01
[download]

which doesn't do exactly what you want (I can't see exactly what you want in any case), but should get you going.