Regular expression not working as expected for special characters

Question

I have a Wireshark capture and I'm trying to create a display filter [Wireshark documentation] that finds XML documents which contain the term @@ V? (at-at-space-V-questionmark). The documentation says Perl Regex are used:

The matches operator makes it possible to search for text in string fields and byte sequences using a regular expression, using Perl regular expression syntax.

And

Note: Wireshark needs to be built with libpcre in order to be able to use the matches operator.

I can't find out whether this condition applies, but in general I can use the matches operator, so I'd assume that part is fulfilled.

IMHO the filter xml matches "@@ V\?" should work, but it finds XML that does not fit the criterion, e.g. an XML like

<?xml version="1.0"?>
<dialog><sysdef name="TERMREC" value="@@ U1160613113912"/></dialog>

What's wrong with my filter or with Wireshark?

Using a filter without special characters (e.g. xml matches "@@ V0") works as expected. Other filters with special characters (e.g. xml matches "@@ V1\*") do not work as well.

Answer 1

It turns out that I have to use a double backslash, e.g. xml matches "@@ V\\?" and xml matches "@@ V1\\*".

I knew this has to be done in code like C++ or C#, but didn't expect this in a user input field. Especially, I wonder why an invalid expression with a single backslash does not result in an error but provides false results instead.

I have opened Wireshark Bug 12522.