For lengthy and complex reasons that we will not get into, can there be any reason you cannot begin a 'directory' having a + ?

For instance

http://stackoverflow.com/+helloworld

Observe that it isn't really a directory, it's being planned utilizing a rewriterule

Just checking...

?

+Note : Like the old-fashioned tilda ~ but I'd rather not use ~ because nobody knows where it's around the keyboard

No you can't utilize it to touch on, generally symbol + in URL describes whitespace: http://trprod.proofstat.com/homepages/webcatalog/cec/specs/special_c.htm

Have you try with this particular?

rewriterule ^\+helloworld$ /test.html