Reword RSC15f to remove confusion about storage of a successful fallback host

Author: paddybyers

content/client-lib-development-guide/features.textile

@@ -90,7 +90,7 @@ h3(#restclient). RestClient
 ** @(RSC15e)@ The primary host is by default @rest.ably.io@ (unless overriden in @ClientOptions#environment@ or @ClientOptions#restHost@), which, through DNS, is automatically routed to the client's closest data center. New HTTP requests (except where @RSC15f@ applies and a cached fallback host is in effect) are first attempted against the primary host.
 ** @(RSC15a)@ In the case of an error necessitating use of an alternative host (see "RSC15d":#RSC15d), try fallback hosts (with a matching Host header as this is necessary when fallbacks are proxied through a CDN) in random order, continuing to try further hosts if "qualifying errors":#RSC15d occur, failing when all have been tried or the configured @httpMaxRetryCount@ has been reached (see "TO3l@":#TO3l5). This ensures that a client library is able to work around routing or other problems for the user's closest data center. For example, if a @POST@ request to @rest.ably.io@ fails because the default endpoint is unreachable or unserviceable, then the @POST@ request should be retried again against the fallback hosts in attempt to find an alternate healthy data center to service the request. The five default fallback hosts are @[a-e].ably-realtime.com@. If an array of custom fallback hosts are provided in @ClientOptions#fallbackHosts@, then they will be used instead. If an empty array of fallback hosts is provided, then fallback host functionality is disabled
 ** @(RSC15d)@ Errors that necessitate use of an alternative host include: host unresolvable or unreachable, request timeout, or a response but with an applicable HTTP status code in the range @500 <= code <= 504@. Resending requests that have failed for other failure conditions will not fix the problem and will simply increase the load on other data-centers unnecessarily
-** @(RSC15f)@ Once/if a given fallback host succeeds, it should be stored for the @fallbackRetryTimeout@ in @ClientOptions@. Future HTTP requests during that period should use that host. If during this period a "qualifying errors":#RSC15d occurs on that host, or after @fallbackRetryTimeout@ has expired, it should be unstored, and the fallback sequence begun again from scratch, starting with the default primary host (@rest.ably.io@ or @ClientOptions#restHost@)
+** @(RSC15f)@ Once/if a given fallback host succeeds, the client should store that successful fallback host for @ClientOptions.fallbackRetryTimeout@. Future HTTP requests during that period should use that host. If during this period a "qualifying errors":#RSC15d occurs on that host, or after @fallbackRetryTimeout@ has expired, it should be unstored, and the fallback sequence begun again from scratch, starting with the default primary host (@rest.ably.io@ or @ClientOptions#restHost@)
 * @(RSC17)@ When instancing the library, if a @clientId@ attribute is set in @ClientOptions@, then the @Auth#clientId@ attribute will contain the provided @clientId@
 * @(RSC19)@ @RestClient#request@ function is provided as a convenience for customers who wish to use bleeding edge REST API functionality that is either not documented or is not included in the API for our client libraries. The REST client library provides a function to issue HTTP requests to the Ably endpoints with all the built in functionality of the library such as authentication, paging, fallback hosts, MsgPack and JSON support etc. The function:
 ** @(RSC19a)@ Method signature is @request(string method, string path, Dict<String, String> params?, JsonObject | JsonArray body?, Dict<String, String> headers?) -> HttpPaginatedResponse@ with arguments: @method@ is a valid "HTTP verb":https://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html (must support @"GET"@, @"POST"@, and @"PUT"@, should support @"PATCH"@ and @"DELETE", may support others); @path@ is the path component of the URL such as @"/channels"@; @params@ and @headers@ are optional arguments containing pairs of key value strings (multi-valued headers are not supported) that will result in query params and HTTP headers being added respectively in the request (the argument types can be idiomatic for the language such as @Object@ in the case of Javascript); @body@ is an optional @JsonObject@ or @JsonArray@ like object argument that can be easily serialized to MsgPack or JSON