diff --git a/src/Loop.php b/src/Loop.php
index 92795744..6c81530d 100644
--- a/src/Loop.php
+++ b/src/Loop.php
@@ -129,10 +129,14 @@ public static function stop()
     /**
      * Defer the execution of a callback.
      *
-     * @param callable(string $watcherId, mixed $data) $callback The callback to defer.
+     * The deferred callable MUST be executed in the next tick of the event loop and before any other type of watcher.
+     * Order of enabling MUST be preserved when executing the callbacks.
+     *
+     * @param callable(string $watcherId, mixed $data) $callback The callback to defer. The `$watcherId` will be
+     *     invalidated before the callback call.
      * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function defer(callable $callback, $data = null)
     {
@@ -143,13 +147,15 @@ public static function defer(callable $callback, $data = null)
     /**
      * Delay the execution of a callback.
      *
-     * The delay is a minimum and approximate, accuracy is not guaranteed.
+     * The delay is a minimum and approximate, accuracy is not guaranteed. Order of calls MUST be determined by which
+     * timers expire first, but timers with the same expiration time MAY be executed in any order.
      *
-     * @param int $time The amount of time, in milliseconds, to delay the execution for.
-     * @param callable(string $watcherId, mixed $data) $callback The callback to delay.
+     * @param int $delay The amount of time, in milliseconds, to delay the execution for.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to delay. The `$watcherId` will be
+     *     invalidated before the callback call.
      * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function delay($time, callable $callback, $data = null)
     {
@@ -160,14 +166,15 @@ public static function delay($time, callable $callback, $data = null)
     /**
      * Repeatedly execute a callback.
      *
-     * The interval between executions is a minimum and approximate, accuracy is not guaranteed.
+     * The interval between executions is a minimum and approximate, accuracy is not guaranteed. Order of calls MUST be
+     * determined by which timers expire first, but timers with the same expiration time MAY be executed in any order.
      * The first execution is scheduled after the first interval period.
      *
      * @param int $interval The time interval, in milliseconds, to wait between executions.
      * @param callable(string $watcherId, mixed $data) $callback The callback to repeat.
      * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function repeat($interval, callable $callback, $data = null)
     {
@@ -178,11 +185,18 @@ public static function repeat($interval, callable $callback, $data = null)
     /**
      * Execute a callback when a stream resource becomes readable or is closed for reading.
      *
+     * Warning: Closing resources locally, e.g. with `fclose`, might not invoke the callback. Be sure to `cancel` the
+     * watcher when closing the resource locally. Drivers MAY choose to notify the user if there are watchers on invalid
+     * resources, but are not required to, due to the high performance impact. Watchers on closed resources are
+     * therefore undefined behavior.
+     *
+     * Multiple watchers on the same stream MAY be executed in any order.
+     *
      * @param resource $stream The stream to monitor.
      * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function onReadable($stream, callable $callback, $data = null)
     {
@@ -193,11 +207,18 @@ public static function onReadable($stream, callable $callback, $data = null)
     /**
      * Execute a callback when a stream resource becomes writable or is closed for writing.
      *
+     * Warning: Closing resources locally, e.g. with `fclose`, might not invoke the callback. Be sure to `cancel` the
+     * watcher when closing the resource locally. Drivers MAY choose to notify the user if there are watchers on invalid
+     * resources, but are not required to, due to the high performance impact. Watchers on closed resources are
+     * therefore undefined behavior.
+     *
+     * Multiple watchers on the same stream MAY be executed in any order.
+     *
      * @param resource $stream The stream to monitor.
      * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      */
     public static function onWritable($stream, callable $callback, $data = null)
     {
@@ -208,16 +229,19 @@ public static function onWritable($stream, callable $callback, $data = null)
     /**
      * Execute a callback when a signal is received.
      *
-     * WARNING: Installing a handler on the same signal on different scopes of event loop execution is
-     * undefined behavior and may break things arbitrarily.
+     * Warning: Installing the same signal on different instances of this interface is deemed undefined behavior.
+     * Implementations MAY try to detect this, if possible, but are not required to. This is due to technical
+     * limitations of the signals being registered globally per process.
+     *
+     * Multiple watchers on the same signal MAY be executed in any order.
      *
      * @param int $signo The signal number to monitor.
      * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.
-     * @param mixed $data Arbitrary data given to the callback function as the `$data` parameter.
+     * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
-     * @return string An identifier that can be used to cancel, enable or disable the watcher.
+     * @return string An unique identifier that can be used to cancel, enable or disable the watcher.
      *
-     * @throws UnsupportedFeatureException Thrown if signal handling is not supported.
+     * @throws UnsupportedFeatureException If signal handling is not supported.
      */
     public static function onSignal($signo, callable $callback, $data = null)
     {
@@ -228,11 +252,15 @@ public static function onSignal($signo, callable $callback, $data = null)
     /**
      * Enable a watcher.
      *
+     * Watchers (enabling or new watchers) MUST immediately be marked as enabled, but only be activated (i.e. callbacks
+     * can be called) right before the next tick. Callbacks of watchers MUST not be called in the tick they were
+     * enabled.
+     *
      * @param string $watcherId The watcher identifier.
      *
      * @return void
      *
-     * @throws InvalidWatcherException Thrown if the watcher identifier is invalid.
+     * @throws InvalidWatcherException If the watcher identifier is invalid.
      */
     public static function enable($watcherId)
     {
@@ -243,6 +271,9 @@ public static function enable($watcherId)
     /**
      * Disable a watcher.
      *
+     * Disabling a watcher MUST NOT invalidate the watcher. Calling this function MUST NOT fail, even if passed an
+     * invalid watcher.
+     *
      * @param string $watcherId The watcher identifier.
      *
      * @return void
@@ -256,8 +287,8 @@ public static function disable($watcherId)
     /**
      * Cancel a watcher.
      *
-     * This will detatch the event loop from all resources that are associated to the watcher. After this
-     * operation the watcher is permanently invalid.
+     * This will detatch the event loop from all resources that are associated to the watcher. After this operation the
+     * watcher is permanently invalid. Calling this function MUST NOT fail, even if passed an invalid watcher.
      *
      * @param string $watcherId The watcher identifier.
      *
@@ -272,8 +303,8 @@ public static function cancel($watcherId)
     /**
      * Reference a watcher.
      *
-     * This will keep the event loop alive whilst the watcher is still being monitored. Watchers have this state
-     * by default.
+     * This will keep the event loop alive whilst the watcher is still being monitored. Watchers have this state by
+     * default.
      *
      * @param string $watcherId The watcher identifier.
      *
@@ -290,8 +321,8 @@ public static function reference($watcherId)
     /**
      * Unreference a watcher.
      *
-     * The event loop should exit the run method when only unreferenced watchers are still being monitored.
-     * Watchers are all referenced by default.
+     * The event loop should exit the run method when only unreferenced watchers are still being monitored. Watchers
+     * are all referenced by default.
      *
      * @param string $watcherId The watcher identifier.
      *
@@ -309,8 +340,7 @@ public static function unreference($watcherId)
      * Stores information in the loop bound registry.
      *
      * This can be used to store loop bound information. Stored information is package private. Packages MUST NOT
-     * retrieve the stored state of other packages. Packages MUST use the following prefix to keys:
-     * `vendor.package.`
+     * retrieve the stored state of other packages. Packages MUST use the following prefix for keys: `vendor.package.`
      *
      * @param string $key The namespaced storage key.
      * @param mixed $value The value to be stored.
@@ -326,12 +356,12 @@ public static function setState($key, $value)
     /**
      * Gets information stored bound to the loop.
      *
-     * Stored information is package private. Packages MUST NOT retrieve the stored state of other packages.
-     * Packages MUST use the following prefix to keys: `vendor.package.`
+     * Stored information is package private. Packages MUST NOT retrieve the stored state of other packages. Packages
+     * MUST use the following prefix for keys: `vendor.package.`
      *
      * @param string $key The namespaced storage key.
      *
-     * @return mixed previously stored value or null if it doesn't exist
+     * @return mixed The previously stored value or `null` if it doesn't exist.
      */
     public static function getState($key)
     {
diff --git a/src/Loop/Driver.php b/src/Loop/Driver.php
index 4c69389b..0a22cb79 100644
--- a/src/Loop/Driver.php
+++ b/src/Loop/Driver.php
@@ -66,7 +66,7 @@ abstract public function delay($delay, callable $callback, $data = null);
      * Repeatedly execute a callback.
      *
      * The interval between executions is a minimum and approximate, accuracy is not guaranteed. Order of calls MUST be
-     * determined by which timers expire first, but timers with the same expiration time may be executed in any order.
+     * determined by which timers expire first, but timers with the same expiration time MAY be executed in any order.
      * The first execution is scheduled after the first interval period.
      *
      * @param int $interval The time interval, in milliseconds, to wait between executions.
@@ -80,7 +80,12 @@ abstract public function repeat($interval, callable $callback, $data = null);
     /**
      * Execute a callback when a stream resource becomes readable or is closed for reading.
      *
-     * Multiple watchers on the same stream may be executed in any order.
+     * Warning: Closing resources locally, e.g. with `fclose`, might not invoke the callback. Be sure to `cancel` the
+     * watcher when closing the resource locally. Drivers MAY choose to notify the user if there are watchers on invalid
+     * resources, but are not required to, due to the high performance impact. Watchers on closed resources are
+     * therefore undefined behavior.
+     *
+     * Multiple watchers on the same stream MAY be executed in any order.
      *
      * @param resource $stream The stream to monitor.
      * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
@@ -93,7 +98,12 @@ abstract public function onReadable($stream, callable $callback, $data = null);
     /**
      * Execute a callback when a stream resource becomes writable or is closed for writing.
      *
-     * Multiple watchers on the same stream may be executed in any order.
+     * Warning: Closing resources locally, e.g. with `fclose`, might not invoke the callback. Be sure to `cancel` the
+     * watcher when closing the resource locally. Drivers MAY choose to notify the user if there are watchers on invalid
+     * resources, but are not required to, due to the high performance impact. Watchers on closed resources are
+     * therefore undefined behavior.
+     *
+     * Multiple watchers on the same stream MAY be executed in any order.
      *
      * @param resource $stream The stream to monitor.
      * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
@@ -106,12 +116,12 @@ abstract public function onWritable($stream, callable $callback, $data = null);
     /**
      * Execute a callback when a signal is received.
      *
-     * Multiple watchers on the same signal may be executed in any order.
-     *
-     * NOTE: Installing the same signal on different instances of this interface is deemed undefined behavior.
-     * Implementations may try to detect this, if possible, but are not required to. This is due to technical
+     * Warning: Installing the same signal on different instances of this interface is deemed undefined behavior.
+     * Implementations MAY try to detect this, if possible, but are not required to. This is due to technical
      * limitations of the signals being registered globally per process.
      *
+     * Multiple watchers on the same signal MAY be executed in any order.
+     *
      * @param int $signo The signal number to monitor.
      * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
@@ -267,7 +277,7 @@ abstract public function info();
      *
      * Example: the `uv_loop` resource for `libuv` or the `EvLoop` object for `libev` or `null` for a native driver.
      *
-     * NOTE: This function is *not* exposed in the `Loop` class. Users shall access it directly on the respective loop
+     * Note: This function is *not* exposed in the `Loop` class. Users shall access it directly on the respective loop
      * instance.
      *
      * @return null|object|resource The loop handle the event loop operates on. `null` if there is none.