A unique identifier for the TextChatMessage.

A general purpose field for storing miscellaneous data about the TextChatMessage. The second argument of TextChannel:SendAsync() and TextChannel:DisplaySystemMessage() is used to populate this field.

Use this field to apply additional formatting for special messages within TextChatService.OnIncomingMessage and TextChannel.OnIncomingMessage callbacks.

local TextChatService = game:GetService("TextChatService")

local generalChannel: TextChannel = TextChatService:WaitForChild("TextChannels").RBXGeneral

generalChannel:DisplaySystemMessage("This is an error!", "Game.Error.Generic")
generalChannel:DisplaySystemMessage("Could not find save data!", "Game.Error.SaveDataNotFound")

generalChannel:DisplaySystemMessage("You won the game!", "Game.Info.Win")
generalChannel:DisplaySystemMessage("You lost the game!", "Game.Info.Lose")

generalChannel.OnIncomingMessage = function(message: TextChatMessage)
	if string.find(message.Metadata, "Error") then
		local overrideProperties = Instance.new("TextChatMessageProperties")
		overrideProperties.TextColor = Color3.fromRGB(255, 0, 0)
		return overrideProperties
	elseif string.find(message.Metadata, "Info") then
		local overrideProperties = Instance.new("TextChatMessageProperties")
		overrideProperties.TextColor = Color3.fromRGB(0, 255, 150)
		return overrideProperties
	end

	return nil
end

As follows is a reference of the default system messages emitted by the chat system:

A prefix to add to a user's message. This supports Rich Text, so developers can set custom properties for this text to support chat tags.

By default, TextChatMessage.PrefixText is the name of the TextSource, which is the Player.DisplayName of the user associated with the TextSource via TextSource.UserId.

Indicates the status of the TextChatMessage.

The filtered text message for the user. Different users may receive different strings from this property based on filtering rules. It can be an empty string.

A reference to the origin TextChannel.

A reference to the origin TextSource.

A timestamp of when the message was originally sent.

Represents translated and filtered text messages based on users' localization settings. The system doesn't translate messages between users with the same localization settings or using languages without the text filter support, so this property can be an empty string if no translation happens. For customization, see Customizing Translated Messages.