I've often found myself wanting to indent a pretty-printed expression in it's entirety, e.g. when surrounding it by other text, as part of an error output.

Would you accept a PR that added an outputOptionsInitialIndent field (feel free to bikeshed the name) to OutputOptions?

I haven't yet looked at the code, but I imagine #25 would make this very easy, if it isn't already, as it would just amount to running with a non-zero in the initial state.