svn diff -x --unified

How do I supply the number of context lines for unified diff?

$ svn diff --help
seems to imply that "svn diff -x --unified" is what I need.
However, there seems to be no way to pass "--unified=1" to the external
diff program:

$ svn di -x '--unified 1' my-file-name
svn: Invalid argument '1' in diff options
$ svn di -x --unified 1 my-file-name
svn: '1' is not under version control
$ svn di -x --unified -x 1 my-file-name
svn: Invalid argument '1' in diff options
$ svn di -x --unified=1 my-file-name
svn: Error parsing diff options: Missing parameter for the specified command line option
$ svn di -x --unified 1 my-file-name
svn: '1' is not under version control
$ svn di -x -u1 my-file-name
svn: Error parsing diff options: Bad character specified on command line

thanks!

-- 
Sam Steingold (http://sds.podval.org/) on CentOS release 5.5 (Final) X
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