Updating policy query parameter language to be clearer.

Author: janedotx

policy/README.md

@@ -128,10 +128,10 @@ Authorization is not required and agencies are encouraged to make these endpoint
 | Name         | Type      | Required / Optional | Description                                    |
 | ------------ | --------- | --- | ---------------------------------------------- |
 | `id`         | UUID      | Optional    | If provided, returns one policy object with the matching UUID; default is to return all policy objects.                       |
-| `start_date` | [timestamp][ts] | Optional    | Earliest effective date; default is policies effective as of the request time |
-| `end_date`   | [timestamp][ts] | Optional    | Latest effective date; default is all policies effective in the future    |
+| `start_date` | [timestamp][ts] | Optional    | Beginning date of the queried time range; the default value is the request time |
+| `end_date`   | [timestamp][ts] | Optional    | Ending date of the queried time range; the default value is null, which captures all policies that are effective in the future|
 
-`start_date` and `end_date` are only considered when no `id` parameter is provided.
+`start_date` and `end_date` are only considered when no `id` parameter is provided. They should return any policy whose effectiveness overlaps with or is contained with this range. Suppose there's a policy with a `start_date` of 1/1/21 and `end_date` of 1/31/21. Assuming an `end_date` that is null, 12/1/20 and 1/5/21 `start_dates` will return the policy, but 2/10/21 wouldn't. Assuming a `start_date` parameter of say, 11/1/20, then an `end_date` of 12/1/20 wouldn't return the policy, but 1/5/21 and 2/10/21 would. Lastly, a `start_date` of 1/5/21 and `end_date` of 1/6/21 would also return the policy. Please note also that while dates in the format MM:DD:YY are being used here, `start_date` and `end_date` must be numbers representing milliseconds since the Unix epoch time.
 
 Policies will be returned in order of effective date (see schema below), with pagination as in the `agency` and `provider` specs.