URLencoding or XML Output Encoding??

I know there is no built in url encoding function.

However,

I have read that you can set a particular encoding for the xml document that will convert URLs with spaces and such.
I haven't found anything telling me what exact encoding to use.

Also,

I have read that you can create a namespace and use the php like URLencode() function in your xml documents.

If this is so then does anyone know how to preform this?

Thanks bunches!