Column name to the values to match. A company matches when every key matches (keys are AND'd), and a key matches when the column holds any of its values (values are OR'd). Filterable columns are those with an index; a filter on any other column (free text such as company_description, or floating point such as address_latitude) is refused with a 400 that lists the filterable columns. A value that is not of the column's type (e.g. "abc" for global_headcount) is also a 400.