The Search docs for geoValue don't specify acceptable formats: they link to a Wiki page of what is basically all known ways humans have ever spelled latitude and longitude.

Strawman: we expect a tuple of two floats, where positive/negative represent degrees North / South of the equator (for latitude) and East / West of Greenwich (for longitude). Or else we take any string, require the user to pass in a field_type argument to use geoValue, and just let the server barf if it doesn't like the string.