if ( /<gene_seq ([^>]+)>/ ) 
{
    my $attribString = $1;

# The challenge is to split the line properly into key/val
# pairs; first, let's get rid of boundary stuff that might
# get in the way:

    $attribString =~ s{^\s+}{}; # initial whitespace
    $attribString =~ s{[/\s]+$}{}; # final whitespace and/or "/"

# now split into key,val pairs, assuming that " = " falls
# between attrib name and attrib value, while the boundary
# between a value and the next attrib name is whitespace
# preceded by double-quote and followed by alphanumeric:

    my %attribHash = split( /\s+=\s+|(?<=\w\")\s+(?=\w)/, $attribString );

# That's it; now work with the keys and values of that hash...

##</code><code>##

    die "Bad xml tag:\n$_\n" if ( grep( /\"/, keys %attribHash );