docs: clarify afterRequest successful/failed reflect responseHandling rule (#3440)

The htmx:afterRequest docs described `detail.successful` and `detail.failed`
purely in terms of "20x status code", but the actual logic uses the matched
htmx.config.responseHandling rule's `error` flag. When users customize
responseHandling to allow non-2xx responses to swap (e.g.
`{"code":"...", "swap": true}` without `error: true`), those responses are
also marked `successful` — a behavior that surprised the issue reporter.

Updates the descriptions of both detail.successful and detail.failed to
accurately reference responseHandling, while preserving the default
"20x = successful" framing as a parenthetical default-behavior note.
Adds an explicit note about the custom responseHandling case.

No code change; this aligns documentation with the existing intentional
behavior confirmed by @MichaelWest22 in the issue.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: manwithacat

www/content/events.md

@@ -48,10 +48,14 @@ can be paired with [`htmx:beforeRequest`](#htmx:beforeRequest) to wrap behavior
 * `detail.xhr` - the `XMLHttpRequest`
 * `detail.target` - the target of the request
 * `detail.requestConfig` - the configuration of the AJAX request
-* `detail.successful` - true if the response has a 20x status code or is marked `detail.isError = false` in the
-  `htmx:beforeSwap` event, else false
-* `detail.failed` - true if the response does not have a 20x status code or is marked `detail.isError = true` in the
-  `htmx:beforeSwap` event, else false
+* `detail.successful` - true if the response is not marked as an error by the matched
+  [`htmx.config.responseHandling`](@/docs.md#response-handling) rule (by default, a 20x status code) or is marked
+  `detail.isError = false` in the `htmx:beforeSwap` event, else false. Note that if you customize
+  `responseHandling` to allow non-2xx codes to swap (e.g. `{"code":"...", "swap": true}` without `error: true`),
+  those responses will also be marked `successful` here.
+* `detail.failed` - true if the response is marked as an error by the matched
+  [`htmx.config.responseHandling`](@/docs.md#response-handling) rule (by default, a non-20x status code) or is marked
+  `detail.isError = true` in the `htmx:beforeSwap` event, else false
 
 ### Event - `htmx:afterSettle` {#htmx:afterSettle}