diff --git a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
index af5152c68..cda099b25 100644
--- a/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
+++ b/mirai-core-qqandroid/src/commonMain/kotlin/net/mamoe/mirai/qqandroid/QQAndroidBot.common.kt
@@ -24,10 +24,7 @@ import kotlinx.serialization.UnstableDefault
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.JsonConfiguration
 import kotlinx.serialization.json.int
-import net.mamoe.mirai.Bot
-import net.mamoe.mirai.BotImpl
-import net.mamoe.mirai.LowLevelAPI
-import net.mamoe.mirai.ThisApiMustBeUsedInWithConnectionLockBlock
+import net.mamoe.mirai.*
 import net.mamoe.mirai.contact.*
 import net.mamoe.mirai.data.*
 import net.mamoe.mirai.event.broadcast
@@ -82,10 +79,18 @@ internal class QQAndroidBot constructor(
 
     @OptIn(LowLevelAPI::class)
     override suspend fun acceptNewFriendRequest(event: NewFriendRequestEvent) {
+        check(event.bot === this) {
+            "the request $event is from Bot ${event.bot.id} but you are responding with bot ${this.id}"
+        }
+
         check(event.responded.compareAndSet(false, true)) {
             "the request $this has already been responded"
         }
 
+        check(!friends.contains(event.fromId)) {
+            "the request $event is outdated: You had already responded it on another device."
+        }
+
         network.run {
             NewContact.SystemMsgNewFriend.Action(
                 bot.client,
@@ -100,8 +105,16 @@ internal class QQAndroidBot constructor(
     }
 
     override suspend fun rejectNewFriendRequest(event: NewFriendRequestEvent, blackList: Boolean) {
+        check(event.bot === this) {
+            "the request $event is from Bot ${event.bot.id} but you are responding with bot ${this.id}"
+        }
+
         check(event.responded.compareAndSet(false, true)) {
-            "the request $this has already been responded"
+            "the request $event has already been responded"
+        }
+
+        check(!friends.contains(event.fromId)) {
+            "the request $event is outdated: You had already responded it on another device."
         }
 
         network.run {
@@ -116,10 +129,16 @@ internal class QQAndroidBot constructor(
 
     @OptIn(LowLevelAPI::class)
     override suspend fun acceptMemberJoinRequest(event: MemberJoinRequestEvent) {
+        @Suppress("DuplicatedCode")
+        checkGroupPermission(event.bot, event.group) { event::class.simpleName ?: "<anonymous class>" }
         check(event.responded.compareAndSet(false, true)) {
             "the request $this has already been responded"
         }
 
+        check(!event.group.members.contains(event.fromId)) {
+            "the request $this is outdated: Another operator has already responded it."
+        }
+
         network.run {
             NewContact.SystemMsgNewGroup.Action(
                 bot.client,
@@ -137,11 +156,17 @@ internal class QQAndroidBot constructor(
         }
     }
 
+    @Suppress("DuplicatedCode")
     @OptIn(LowLevelAPI::class)
     override suspend fun rejectMemberJoinRequest(event: MemberJoinRequestEvent, blackList: Boolean) {
+        checkGroupPermission(event.bot, event.group) { event::class.simpleName ?: "<anonymous class>" }
         check(event.responded.compareAndSet(false, true)) {
             "the request $this has already been responded"
         }
+
+        check(!event.group.members.contains(event.fromId)) {
+            "the request $this is outdated: Another operator has already responded it."
+        }
         network.run {
             NewContact.SystemMsgNewGroup.Action(
                 bot.client,
@@ -152,7 +177,22 @@ internal class QQAndroidBot constructor(
         }
     }
 
+    private inline fun checkGroupPermission(eventBot: Bot, eventGroup: Group, eventName: () -> String) {
+        val group = this.getGroupOrNull(eventGroup.id)
+            ?: kotlin.run {
+                if (this == eventBot) {
+                    error("A ${eventName()} is outdated. Group ${eventGroup.id} not found for bot ${this.id}. " +
+                            "This is because bot isn't in the group anymore")
+                } else {
+                    error("A ${eventName()} is from bot ${eventBot.id}, but you are trying to respond it using bot ${this.id} who isn't a member of the group ${eventGroup.id}")
+                }
+            }
+
+        group.checkBotPermissionOperator()
+    }
+
     override suspend fun ignoreMemberJoinRequest(event: MemberJoinRequestEvent, blackList: Boolean) {
+        checkGroupPermission(event.bot, event.group) { event::class.simpleName ?: "<anonymous class>" }
         check(event.responded.compareAndSet(false, true)) {
             "the request $this has already been responded"
         }
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
index dd690c85f..78897648c 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/MessageReceipt.kt
@@ -44,7 +44,7 @@ import kotlin.jvm.JvmSynthetic
 @OptIn(MiraiInternalAPI::class)
 open class MessageReceipt<out C : Contact>(
     /**
-     * 指代发送出去的消息
+     * 指代发送出去的消息.
      */
     val source: OnlineMessageSource.Outgoing,
     /**
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt
index d5385162d..6a127cc42 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/AtAll.kt
@@ -12,11 +12,9 @@
 
 package net.mamoe.mirai.message.data
 
-import net.mamoe.mirai.utils.MiraiInternalAPI
 import net.mamoe.mirai.utils.SinceMirai
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
-import kotlin.jvm.JvmSynthetic
 
 private const val displayA = "@全体成员"
 
@@ -50,15 +48,6 @@ object AtAll :
     }
 
     // 自动为消息补充 " "
-    @OptIn(MiraiInternalAPI::class)
-    @Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
-    @Suppress("INAPPLICABLE_JVM_NAME", "EXPOSED_FUNCTION_RETURN_TYPE")
-    @JvmName("followedBy")
-    @JvmSynthetic
-    override fun followedBy1(tail: Message): CombinedMessage {
-        return followedByInternalForBinaryCompatibility(tail)
-    }
-
     override fun followedBy(tail: Message): MessageChain {
         if (tail is PlainText && tail.stringValue.startsWith(' ')) {
             return super.followedBy(tail)
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/HummerMessage.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/HummerMessage.kt
index cb544f1f1..edb23949a 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/HummerMessage.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/HummerMessage.kt
@@ -8,6 +8,8 @@
  */
 
 @file:Suppress("unused", "NOTHING_TO_INLINE")
+@file:JvmMultifileClass
+@file:JvmName("MessageUtils") // since 0.39.1
 
 package net.mamoe.mirai.message.data
 
@@ -15,10 +17,7 @@ import net.mamoe.mirai.message.data.PokeMessage.Types
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.MiraiInternalAPI
 import net.mamoe.mirai.utils.SinceMirai
-import kotlin.jvm.JvmField
-import kotlin.jvm.JvmName
-import kotlin.jvm.JvmStatic
-import kotlin.jvm.JvmSynthetic
+import kotlin.jvm.*
 
 /**
  * 一些特殊的消息
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt
index 33140a9e2..634ad1c04 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Image.kt
@@ -19,7 +19,6 @@ import net.mamoe.mirai.Bot
 import net.mamoe.mirai.BotImpl
 import net.mamoe.mirai.contact.Contact
 import net.mamoe.mirai.contact.Group
-import net.mamoe.mirai.utils.ExternalImage
 import net.mamoe.mirai.utils.MiraiInternalAPI
 import net.mamoe.mirai.utils.PlannedRemoval
 import net.mamoe.mirai.utils.SinceMirai
@@ -38,7 +37,7 @@ import kotlin.jvm.JvmSynthetic
  *
  * ### [toString] 和 [contentToString]
  * - [toString] 固定返回 `[mirai:image:<ID>]` 格式字符串, 其中 `<ID>` 代表 [imageId].
- * - [contentToString] 固定返回 `"[图片]"`
+ * - [contentToString] 固定返回 ```"[图片]"```
  *
  * ### 上传和发送图片
  * @see Contact.uploadImage 上传 [图片文件][ExternalImage] 并得到 [Image] 消息
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
index b0bbc6b29..a9d428bd6 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/Message.kt
@@ -8,6 +8,8 @@
  */
 
 @file:Suppress("MemberVisibilityCanBePrivate", "unused", "EXPERIMENTAL_API_USAGE", "NOTHING_TO_INLINE")
+@file:JvmMultifileClass
+@file:JvmName("MessageUtils")
 
 package net.mamoe.mirai.message.data
 
@@ -17,6 +19,7 @@ import net.mamoe.mirai.message.data.Message.Key
 import net.mamoe.mirai.utils.MiraiInternalAPI
 import net.mamoe.mirai.utils.PlannedRemoval
 import net.mamoe.mirai.utils.SinceMirai
+import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmSynthetic
 
@@ -313,6 +316,8 @@ interface SingleMessage : Message, CharSequence, Comparable<String> {
 /**
  * 消息元数据, 即不含内容的元素.
  *
+ * 所有子类的 [contentToString] 都应该返回空字符串.
+ *
  * @see MessageSource 消息源
  * @see QuoteReply 引用回复
  * @see CustomMessageMetadata 自定义元数据
@@ -328,11 +333,12 @@ interface MessageMetadata : SingleMessage {
 
 /**
  * 约束一个 [MessageChain] 中只存在这一种类型的元素. 新元素将会替换旧元素, 保持原顺序.
+ *
  * 实现此接口的元素将会在连接时自动处理替换.
  */
 @SinceMirai("0.34.0")
 interface ConstrainSingle<out M : Message> : MessageMetadata {
-    val key: Message.Key<M>
+    val key: Key<M>
 }
 
 /**
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
index dc2eb87fc..2cb94afaa 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageChain.kt
@@ -142,9 +142,7 @@ inline fun MessageChain.allContent(block: (MessageContent) -> Boolean): Boolean
     this.forEach {
         if (it !is MessageMetadata) {
             check(it is MessageContent) { "internal error: Message must be either MessageMetaData or MessageContent" }
-            if (!block(it)) {
-                return false
-            }
+            if (!block(it)) return false
         }
     }
     return true
@@ -158,9 +156,7 @@ inline fun MessageChain.noneContent(block: (MessageContent) -> Boolean): Boolean
     this.forEach {
         if (it !is MessageMetadata) {
             check(it is MessageContent) { "internal error: Message must be either MessageMetaData or MessageContent" }
-            if (block(it)) {
-                return false
-            }
+            if (block(it)) return false
         }
     }
     return true
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
index bf590985d..9bc377265 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/MessageSource.kt
@@ -29,6 +29,25 @@ import kotlin.jvm.JvmSynthetic
 /**
  * 消息源, 它存在于 [MessageChain] 中, 用于表示这个消息的来源.
  *
+ *
+ * ### 组成
+ * MessageSource 由 metadata (元数据), form & target, content 组成
+ *
+ * #### metadata
+ * - [id] 消息 id (序列号)
+ * - [internalId] 消息内部 id
+ * - [time] 时间
+ *
+ * 官方客户端通过 metadata 这三个数据定位消息, 撤回和引用回复都是如此.
+ *
+ * #### form & target
+ * - [fromId] 消息发送人
+ * - [targetId] 消息发送目标
+ *
+ * #### content
+ * - [originalMessage] 消息内容
+ *
+ *
  * 消息源可用于 [引用回复][QuoteReply] 或 [撤回][Bot.recall].
  *
  * @see Bot.recall 撤回一条消息
@@ -52,50 +71,74 @@ sealed class MessageSource : Message, MessageMetadata, ConstrainSingle<MessageSo
     abstract val bot: Bot
 
     /**
-     * 消息 id.
-     * 此值在同一会话中唯一且有顺序.
+     * 消息 id (序列号).
+     **
+     * #### 值域
+     * 值的范围约为 [UShort] 的范围.
+     *
+     * #### 顺序
+     * 群消息的 id 由服务器维护. 好友消息的 id 由 mirai 维护.
+     *
+     * - 在同一个群的消息中此值随每条消息递增 1.
+     * - 在好友消息中无法保证每次都递增 1. 也可能会产生大幅跳过的情况.
      */
     abstract val id: Int
 
     /**
-     * 内部 id, 仅用于 [Bot.constructMessageSource]
-     * 值没有顺序, 也可能为 0, 取决于服务器是否提供.
-     * 在事件中和在引用中无法保证同一条消息的 [internalId] 相同.
+     * 内部 id. 仅用于协议模块使用.
      *
-     * 仅用于协议实现.
+     * 在撤回消息和引用回复时均需使用此 id.
+     *
+     * 值没有顺序, 也可能为 0, 取决于服务器是否提供.
+     *
+     * 在事件中和在引用中无法保证同一条消息的 [internalId] 相同.
      */
     @SinceMirai("0.39.0")
     abstract val internalId: Int
 
     /**
      * 发送时间时间戳, 单位为秒.
-     * 撤回好友消息时需要
+     *
+     * 时间戳可能来自服务器, 也可能来自 mirai, 且无法保证两者时间同步.
+     *
+     * 撤回消息时需要此值.
      */
     abstract val time: Int
 
     /**
      * 发送人.
-     * 当 [OnlineMessageSource.Outgoing] 时为 [机器人][Bot.id]
-     * 当 [OnlineMessageSource.Incoming] 时为发信 [目标好友][QQ.id] 或 [群][Group.id]
-     * 当 [OfflineMessageSource] 时为 [机器人][Bot.id], 发信 [目标好友][QQ.id] 或 [群][Group.id] (取决于 [OfflineMessageSource.kind])
+     *
+     * - 当 [OnlineMessageSource.Outgoing] 时为 [机器人][Bot.id]
+     * - 当 [OnlineMessageSource.Incoming] 时为发信 [目标好友][QQ.id] 或 [群][Group.id]
+     * - 当 [OfflineMessageSource] 时为 [机器人][Bot.id], 发信 [目标好友][QQ.id] 或 [群][Group.id] (取决于 [OfflineMessageSource.kind])
      */
     abstract val fromId: Long
 
     /**
-     * 发送目标.
-     * 当 [OnlineMessageSource.Outgoing] 时为发信 [目标好友][QQ.id] 或 [群][Group.id] 或 [临时消息][Member.id]
-     * 当 [OnlineMessageSource.Incoming] 时为 [机器人][Bot.id]
-     * 当 [OfflineMessageSource] 时为 [机器人][Bot.id], 发信 [目标好友][QQ.id] 或 [群][Group.id] 或 [临时消息][Member.id] (取决于 [OfflineMessageSource.kind])
+     * 消息发送目标.
+     *
+     * - 当 [OnlineMessageSource.Outgoing] 时为发信 [目标好友][QQ.id] 或 [群][Group.id] 或 [临时消息][Member.id]
+     * - 当 [OnlineMessageSource.Incoming] 时为 [机器人][Bot.id]
+     * - 当 [OfflineMessageSource] 时为 [机器人][Bot.id], 发信 [目标好友][QQ.id] 或 [群][Group.id] 或 [临时消息][Member.id] (取决于 [OfflineMessageSource.kind])
      */
     abstract val targetId: Long // groupCode / friendUin / memberUin
 
     /**
      * 原消息内容.
+     *
+     * 此属性是 **lazy** 的: 它只会在第一次调用时初始化, 因为需要反序列化服务器发来的整个包, 相当于接收了一条新消息.
      */
     @LazyProperty
     abstract val originalMessage: MessageChain
 
+    /**
+     * 返回 `"[mirai:source:$id,$internalId]"`
+     */
     final override fun toString(): String = "[mirai:source:$id,$internalId]"
+
+    /**
+     * 返回空字符串, 因 [MessageMetadata] 的约束.
+     */
     final override fun contentToString(): String = ""
 }
 
@@ -105,7 +148,8 @@ sealed class MessageSource : Message, MessageMetadata, ConstrainSingle<MessageSo
  * 拥有对象化的 [sender], [target], 也可以直接 [recall] 和 [quote]
  *
  * ### 来源
- * **必定是一个发出去的消息或接收到的消息的 [MessageChain] 中的一个元数据 [MessageMetadata].**
+ * - 当 bot 主动发送消息时, 产生 (由协议模块主动构造) [OnlineMessageSource.Outgoing]
+ * - 当 bot 接收消息时, 产生 (由协议模块根据服务器的提供的信息构造) [OnlineMessageSource.Incoming]
  *
  * #### 机器人主动发送消息
  * 当机器人 [主动发出消息][Member.sendMessage], 将会得到一个 [消息回执][MessageReceipt].
@@ -115,6 +159,8 @@ sealed class MessageSource : Message, MessageMetadata, ConstrainSingle<MessageSo
  * 当机器人接收一条消息 [ContactMessage], 这条消息包含一个 [内向消息源][OnlineMessageSource.Incoming], 代表着接收到的这条消息的来源.
  *
  *
+ * ### 实现
+ * 此类的所有子类都有协议模块实现. 不要自行实现它们, 否则将无法发送
  *
  * @see OnlineMessageSource.toOffline 转为 [OfflineMessageSource]
  */
@@ -144,7 +190,7 @@ sealed class OnlineMessageSource : MessageSource() {
     abstract val subject: Contact
 
     /**
-     * 由 [机器人主动发送消息][Contact.sendMessage] 产生的 [MessageSource]
+     * 由 [机器人主动发送消息][Contact.sendMessage] 产生的 [MessageSource], 可通过 [MessageReceipt] 获得.
      */
     sealed class Outgoing : OnlineMessageSource() {
         companion object Key : Message.Key<Outgoing> {
@@ -266,6 +312,8 @@ sealed class OnlineMessageSource : MessageSource() {
 /**
  * 由一条消息中的 [QuoteReply] 得到的 [MessageSource].
  * 此消息源可能来自一条与机器人无关的消息. 因此无法提供对象化的 `sender` 或 `target` 获取.
+ *
+ * @see buildMessageSource 构建一个 [OfflineMessageSource]
  */
 @SinceMirai("0.33.0")
 abstract class OfflineMessageSource : MessageSource() {
@@ -290,6 +338,9 @@ abstract class OfflineMessageSource : MessageSource() {
     // final override fun toString(): String = "OfflineMessageSource(sender=$senderId, target=$targetId)"
 }
 
+/**
+ * 判断是否是发送给群, 或从群接收的消息的消息源
+ */
 // inline for future removal
 inline fun MessageSource.isAboutGroup(): Boolean {
     return when (this) {
@@ -298,6 +349,9 @@ inline fun MessageSource.isAboutGroup(): Boolean {
     }
 }
 
+/**
+ * 判断是否是发送给临时会话, 或从临时会话接收的消息的消息源
+ */
 inline fun MessageSource.isAboutTemp(): Boolean {
     return when (this) {
         is OnlineMessageSource -> subject is Member
@@ -305,6 +359,9 @@ inline fun MessageSource.isAboutTemp(): Boolean {
     }
 }
 
+/**
+ * 判断是否是发送给好友, 或从好友接收的消息的消息源
+ */
 // inline for future removal
 inline fun MessageSource.isAboutFriend(): Boolean {
     return when (this) {
@@ -315,6 +372,7 @@ inline fun MessageSource.isAboutFriend(): Boolean {
 
 /**
  * 引用这条消息
+ * @see QuoteReply
  */
 fun MessageSource.quote(): QuoteReply {
     @OptIn(MiraiInternalAPI::class)
@@ -323,17 +381,37 @@ fun MessageSource.quote(): QuoteReply {
 
 /**
  * 引用这条消息
+ * @see QuoteReply
  */
 fun MessageChain.quote(): QuoteReply {
     @OptIn(MiraiInternalAPI::class)
     return QuoteReply(this.source as? OnlineMessageSource ?: error("only online messages can be quoted"))
 }
 
+/**
+ * 撤回这条消息. 可撤回自己 2 分钟内发出的消息, 和任意时间的群成员的消息.
+ *
+ * [Bot] 撤回自己的消息不需要权限.
+ * [Bot] 撤回群员的消息需要管理员权限.
+ *
+ * @throws PermissionDeniedException 当 [Bot] 无权限操作时
+ * @throws IllegalStateException 当这条消息已经被撤回时 (仅同步主动操作)
+ *
+ * @see Bot.recall
+ */
 @JvmSynthetic
 suspend inline fun MessageSource.recall() = bot.recall(this)
 
 /**
- * 撤回这条消息
+ * 在一段时间后撤回这条消息. 可撤回自己 2 分钟内发出的消息, 和任意时间的群成员的消息.
+ *
+ * [Bot] 撤回自己的消息不需要权限.
+ * [Bot] 撤回群员的消息需要管理员权限.
+ *
+ * @throws PermissionDeniedException 当 [Bot] 无权限操作时
+ * @throws IllegalStateException 当这条消息已经被撤回时 (仅同步主动操作)
+ *
+ * @see Bot.recall
  */
 @JvmSynthetic
 inline fun MessageSource.recallIn(
@@ -345,7 +423,7 @@ inline fun MessageSource.recallIn(
 
 /**
  * 消息 id.
- * 仅从服务器接收的消息才可以获取 id
+ * 仅从服务器接收的消息才可以获取
  *
  * @see MessageSource.id
  */
@@ -353,6 +431,36 @@ inline fun MessageSource.recallIn(
 inline val MessageChain.id: Int
     get() = this.source.id
 
+/**
+ * 消息内部 id.
+ * 仅从服务器接收的消息才可以获取
+ *
+ * @see MessageSource.id
+ */
+@get:JvmSynthetic
+inline val MessageChain.internalId: Int
+    get() = this.source.internalId
+
+/**
+ * 消息时间.
+ * 仅从服务器接收的消息才可以获取
+ *
+ * @see MessageSource.id
+ */
+@get:JvmSynthetic
+inline val MessageChain.time: Int
+    get() = this.source.time
+
+/**
+ * 消息内部 id.
+ * 仅从服务器接收的消息才可以获取
+ *
+ * @see MessageSource.id
+ */
+@get:JvmSynthetic
+inline val MessageChain.bot: Bot
+    get() = this.source.bot
+
 /**
  * 获取这条消息源
  * 仅从服务器接收的消息才可以获取消息源
@@ -361,9 +469,31 @@ inline val MessageChain.id: Int
 inline val MessageChain.source: MessageSource
     get() = this[MessageSource]
 
+/**
+ * 撤回这条消息. 可撤回自己 2 分钟内发出的消息, 和任意时间的群成员的消息.
+ *
+ * [Bot] 撤回自己的消息不需要权限.
+ * [Bot] 撤回群员的消息需要管理员权限.
+ *
+ * @throws PermissionDeniedException 当 [Bot] 无权限操作时
+ * @throws IllegalStateException 当这条消息已经被撤回时 (仅同步主动操作)
+ *
+ * @see Bot.recall
+ */
 @JvmSynthetic
 suspend inline fun MessageChain.recall() = this.source.recall()
 
+/**
+ * 在一段时间后撤回这条消息. 可撤回自己 2 分钟内发出的消息, 和任意时间的群成员的消息.
+ *
+ * [Bot] 撤回自己的消息不需要权限.
+ * [Bot] 撤回群员的消息需要管理员权限.
+ *
+ * @throws PermissionDeniedException 当 [Bot] 无权限操作时
+ * @throws IllegalStateException 当这条消息已经被撤回时 (仅同步主动操作)
+ *
+ * @see Bot.recall
+ */
 @JvmSynthetic
 inline fun MessageChain.recallIn(
     millis: Long,
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/OfflineMessageSource.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/OfflineMessageSource.kt
index f9aabcbcb..2d9e25fca 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/OfflineMessageSource.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/OfflineMessageSource.kt
@@ -25,6 +25,9 @@ import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 import kotlin.jvm.JvmSynthetic
 
+/**
+ * 将在线消息源转换为离线消息源.
+ */
 @SinceMirai("0.39.0")
 @JvmName("toOfflineMessageSource")
 fun OnlineMessageSource.toOffline(): OfflineMessageSource =
@@ -60,6 +63,14 @@ interface MessageSourceAmender {
     var internalId: Int
 
     var originalMessage: MessageChain
+
+    /** 从另一个 [MessageSource] 中复制 [id], [internalId], [time]*/
+    @SinceMirai("0.39.2")
+    fun metadataFrom(another: MessageSource) {
+        this.id = another.id
+        this.internalId = another.internalId
+        this.time = another.time
+    }
 }
 
 
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/QuoteReply.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/QuoteReply.kt
index 4386e06d7..49d09d586 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/QuoteReply.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/QuoteReply.kt
@@ -15,7 +15,6 @@ package net.mamoe.mirai.message.data
 
 import kotlinx.coroutines.Job
 import net.mamoe.mirai.Bot
-import net.mamoe.mirai.message.MessageReceipt
 import net.mamoe.mirai.utils.MiraiExperimentalAPI
 import net.mamoe.mirai.utils.SinceMirai
 import kotlin.coroutines.CoroutineContext
@@ -29,10 +28,19 @@ import kotlin.jvm.JvmSynthetic
 /**
  * 引用回复.
  *
- * 可以引用一条群消息并发送给一个好友, 或是引用好友消息发送给群.
- * 可以引用自己发出的消息. 详见 [MessageReceipt.quote]
+ * 支持引用任何一条消息发送给任何人.
  *
- * @see MessageSource 获取更多信息
+ * #### [source] 的类型:
+ * - 在发送引用回复时, [source] 类型为 [OnlineMessageSource] 或 [OfflineMessageSource]
+ * - 在接收引用回复时, [source] 类型一定为 [OfflineMessageSource]
+ *
+ * #### 原消息内容
+ * 引用回复的原消息内容完全由 [source] 中 [MessageSource.originalMessage] 控制, 客户端不会自行寻找原消息.
+ *
+ * #### 客户端内跳转
+ * 客户端在跳转原消息时, 会通过 [MessageSource.id] 等 metadata
+ *
+ * @see MessageSource 获取有关消息源的更多信息
  */
 @OptIn(MiraiExperimentalAPI::class)
 @SinceMirai("0.33.0")
@@ -50,26 +58,52 @@ class QuoteReply(val source: MessageSource) : Message, MessageMetadata, Constrai
     override fun hashCode(): Int = source.hashCode()
 }
 
+/**
+ * @see MessageSource.id
+ */
 @get:JvmSynthetic
 inline val QuoteReply.id: Int
     get() = source.id
 
+/**
+ * @see MessageSource.internalId
+ */
+@SinceMirai("0.39.2")
+@get:JvmSynthetic
+inline val QuoteReply.internalId: Int
+    get() = source.internalId
+
+/**
+ * @see MessageSource.fromId
+ */
 @get:JvmSynthetic
 inline val QuoteReply.fromId: Long
     get() = source.fromId
 
+/**
+ * @see MessageSource.targetId
+ */
 @get:JvmSynthetic
 inline val QuoteReply.targetId: Long
     get() = source.targetId
 
+/**
+ * @see MessageSource.originalMessage
+ */
 @get:JvmSynthetic
 inline val QuoteReply.originalMessage: MessageChain
     get() = source.originalMessage
 
+/**
+ * @see MessageSource.time
+ */
 @get:JvmSynthetic
 inline val QuoteReply.time: Int
     get() = source.time
 
+/**
+ * @see MessageSource.bot
+ */
 @get:JvmSynthetic
 inline val QuoteReply.bot: Bot
     get() = source.bot
@@ -78,6 +112,9 @@ inline val QuoteReply.bot: Bot
 @JvmSynthetic
 suspend inline fun QuoteReply.recall() = this.source.recall()
 
+/**
+ * 在一段时间后撤回这条消息.
+ */
 @JvmOverloads
 inline fun QuoteReply.recallIn(
     millis: Long,
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_HummerMessage.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_HummerMessage.kt
new file mode 100644
index 000000000..88dcc2889
--- /dev/null
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_HummerMessage.kt
@@ -0,0 +1,43 @@
+/*
+ * Copyright 2020 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/master/LICENSE
+ */
+
+@file:JvmName("HummerMessageKt")
+@file:Suppress("NOTHING_TO_INLINE")
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.utils.PlannedRemoval
+import net.mamoe.mirai.utils.SinceMirai
+import kotlin.jvm.JvmName
+import kotlin.jvm.JvmSynthetic
+
+
+/*
+因为文件改名为做的兼容
+ */
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("flash")
+@SinceMirai("0.33.0")
+inline fun Image.flash2(): FlashImage = FlashImage(this)
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("flash")
+@JvmSynthetic
+@SinceMirai("0.33.0")
+inline fun GroupImage.flash2(): GroupFlashImage = FlashImage(this) as GroupFlashImage
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("flash")
+@JvmSynthetic
+@SinceMirai("0.33.0")
+inline fun FriendImage.flash2(): FriendFlashImage = FlashImage(this) as FriendFlashImage
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_Message.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_Message.kt
new file mode 100644
index 000000000..364b34e22
--- /dev/null
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/_Message.kt
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2020 Mamoe Technologies and contributors.
+ *
+ * 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
+ * Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
+ *
+ * https://github.com/mamoe/mirai/blob/master/LICENSE
+ */
+
+@file:JvmName("MessageKt")
+@file:Suppress("NOTHING_TO_INLINE")
+
+package net.mamoe.mirai.message.data
+
+import net.mamoe.mirai.utils.PlannedRemoval
+import kotlin.jvm.JvmName
+
+
+/*
+因为文件改名为做的兼容
+ */
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("isPlain")
+inline fun Message.isPlain2(): Boolean = this is PlainText
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("isNotPlain")
+inline fun Message.isNotPlain2(): Boolean = this !is PlainText
+
+@PlannedRemoval("1.0.0")
+@Deprecated("for binary compatibility", level = DeprecationLevel.HIDDEN)
+@JvmName("repeat")
+// inline: for future removal
+inline fun Message.repeat2(count: Int): MessageChain {
+    if (this is ConstrainSingle<*>) {
+        // fast-path
+        return this.asMessageChain()
+    }
+    return buildMessageChain(count) {
+        add(this@repeat2)
+    }
+}
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/builder.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/builder.kt
index 40ec15125..79e0c2777 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/builder.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/builder.kt
@@ -42,6 +42,8 @@ inline fun buildMessageChain(initialSize: Int, block: MessageChainBuilder.() ->
 /**
  * [MessageChain] 构建器.
  * 多个连续的 [String] 会被连接为单个 [PlainText] 以优化性能.
+ *
+ *
  * **注意:** 无并发安全性.
  *
  * @see buildMessageChain 推荐使用
@@ -91,6 +93,7 @@ open class MessageChainBuilder private constructor(
         return addAll(elements.flatten())
     }
 
+    @JvmSynthetic
     operator fun Message.unaryPlus() {
         checkBuilt()
         flushCache()
@@ -98,22 +101,26 @@ open class MessageChainBuilder private constructor(
     }
 
 
+    @JvmSynthetic
     operator fun String.unaryPlus() {
         checkBuilt()
         add(this)
     }
 
+    @JvmSynthetic // they should use add
     operator fun plusAssign(plain: String) {
         checkBuilt()
         withCache { append(plain) }
     }
 
+    @JvmSynthetic // they should use add
     operator fun plusAssign(message: Message) {
         checkBuilt()
         flushCache()
         this.add(message)
     }
 
+    @JvmSynthetic // they should use add
     operator fun plusAssign(message: SingleMessage) { // avoid resolution ambiguity
         checkBuilt()
         flushCache()
@@ -125,6 +132,7 @@ open class MessageChainBuilder private constructor(
         withCache { append(plain) }
     }
 
+    @JvmSynthetic // they should use add
     operator fun plusAssign(charSequence: CharSequence) {
         checkBuilt()
         withCache { append(charSequence) }
diff --git a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/impl.kt b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/impl.kt
index 620a7b5c4..5942f5ed9 100644
--- a/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/impl.kt
+++ b/mirai-core/src/commonMain/kotlin/net.mamoe.mirai/message/data/impl.kt
@@ -311,9 +311,11 @@ internal class SingleMessageChainImpl constructor(
 
 
 @SharedImmutable
+@get:JvmSynthetic
 internal val EMPTY_BYTE_ARRAY = ByteArray(0)
 
 
+@JvmSynthetic
 @Suppress("NOTHING_TO_INLINE") // no stack waste
 internal inline fun Char.hexDigitToByte(): Int {
     return when (this) {
@@ -324,6 +326,7 @@ internal inline fun Char.hexDigitToByte(): Int {
     }
 }
 
+@JvmSynthetic
 internal fun String.skipToSecondHyphen(): Int {
     var count = 0
     this.forEachIndexed { index, c ->
@@ -332,6 +335,7 @@ internal fun String.skipToSecondHyphen(): Int {
     error("cannot find two hyphens")
 }
 
+@JvmSynthetic
 internal fun String.imageIdToMd5(offset: Int): ByteArray {
     val result = ByteArray(16)
     var cur = 0