Using regular expressions to select files when using ant copy task

Hi,

I have 'src' folder and a 'dest' folder.  The 'src' folder has the following files:
1) ans_key.tif
2) arrow.tif
3) eqn_y=x+1.tif
4) re teach.tif
5) ab+cd.tif

I want to copy all files that conform to a naming convention to 'dest' folder.  The rules are simple: only allowed characters in file names are a-z, A-Z, 0-9, dash(-), underscore(_) and period(.).  Which means, I want only files 1 and 2 to be copied over to 'dest'.  For this purpose, I wrote the following build.xml:

<project name="name of project" default="copy_graphics" basedir=".">
    <target name="copy_graphics" description="Copy Graphics">
        <copy overwrite="true" todir="dest">
            <fileset dir="src" includes="**/*.tif">
            <containsregexp expression="^[a-zA-Z0-9\._-]+$"/>
            </fileset>
        </copy>
    </target>
</project>

But it didn't work.  What's more confusing is except for file 2 (arrow.tif ), all others get copied.  

I read in one of the forums that <containsregexp> looks in the content rather than the filename.  So I tried playing around various combinations of:
            <fileset dir="src">
            <filename name="**/^[a-zA-Z0-9\._-]+\.tif$"/>
            </fileset>

That didn't work either.  Can anybody please help?

Thanks!