Document that the Enter key causes the keypress event to fire

This change updates the page for the “keypress” event to match actual
behavior in browsers — by changing the page to state that the event
fires when the Enter key is pressed — not only when a key that produces
a character value is pressed.

See w3c/uievents#183 (comment)
and w3c/uievents#266 (comment)
and w3c/uievents#392

Otherwise, without this change, the information on the “keypress” page
incorrectly doesn’t match actual browser behavior — in that the page
states that the “keypress” event fires _only_ when a key that produces a
character value are pressed, while in fact browsers also fire the event
when the Enter key is pressed.

files/en-us/web/api/element/keypress_event/index.md

@@ -10,9 +10,9 @@ browser-compat: api.Element.keypress_event
 
 {{APIRef}} {{deprecated_header}}
 
-The **`keypress`** event is fired when a key that produces a character value is pressed down.
+The **`keypress`** event is fired either when a key that produces a character value is pressed down, or else when the <kbd>Enter</kbd> is pressed down — including when the <kbd>Enter</kbd> key is pressed down in combination with the <kbd>Shift</kbd> or <kbd>Ctrl</kbd> keys.
 
-Examples of keys that produce a character value are alphabetic, numeric, and punctuation keys. Examples of keys that don't produce a character value are modifier keys such as <kbd>Alt</kbd>, <kbd>Shift</kbd>, <kbd>Ctrl</kbd>, or <kbd>Meta</kbd>.
+Examples of keys that produce a character value are alphabetic, numeric, and punctuation keys. Examples of keys that don't produce a character value are modifier keys such as <kbd>Alt</kbd>, <kbd>Shift</kbd>, <kbd>Ctrl</kbd>, <kbd>Meta</kbd>, <kbd>Esc</kbd>, <kbd>Option</kbd>, or <kbd>⌘</kbd>.
 
 > [!WARNING]
 > Since this event has been deprecated, you should use [`beforeinput`](/en-US/docs/Web/API/Element/beforeinput_event) or [`keydown`](/en-US/docs/Web/API/Element/keydown_event) instead.
@@ -71,6 +71,15 @@ _This interface also inherits properties of its parents, {{domxref("UIEvent")}}
 
 This example logs the {{domxref("KeyboardEvent.code")}} value whenever you press a key after focussing the {{htmlelement("input")}} element.
 
+To see which keys cause a `keypress` event to fire, and which keys don't, try pressing the following:
+
+- letter keys, number keys, and punctuation keys
+- symbol keys such as the <kbd>$</kbd>, <kbd>+</kbd>, <kbd>=</kbd>, <kbd>%</kbd>, and <kbd>+</kbd> keys
+- modifier keys such as the <kbd>Alt</kbd>, <kbd>Shift</kbd>, <kbd>Ctrl</kbd>, <kbd>Meta</kbd>, <kbd>Esc</kbd>, <kbd>Option</kbd>, or <kbd>⌘</kbd> keys
+- the <kbd>Enter</kbd> key
+- the <kbd>Enter</kbd> key in combination with the <kbd>Shift</kbd> or <kbd>Ctrl</kbd> keys
+- the <kbd>Enter</kbd> key in combination with modifier keys other than the <kbd>Shift</kbd> or <kbd>Ctrl</kbd> keys
+
 ```html
 <div>
   <label for="sample">Focus the input and type something:</label>