“Kept” means the difference is intentional and will not be aligned with BDFD.

Differences kept on purpose

Function	Bot Creator	BDFD wiki
$useChannel in a slash command	Also redirects the main response; the interaction gets no reply. Use $channelSendMessage[channelID;text] to answer and write elsewhere.	Does not redirect the response of a slash command.
$noMention	Cuts all notifications of the response, including <@id> written on purpose. Add $allowUserMentions[ID] or $allowRoleMentions[ID] to notify someone.	Only removes the automatic mention of the author; written mentions still notify.
$removeContains	Removes a pattern from a text; the form [word;...;amount] is refused. Nothing is deleted from the channel.	Purges recent messages that contain the words.
$ignoreTriggerCase	Accepted, no effect: prefix command names and aliases already ignore case.	Makes triggers case-insensitive (premium).
$alternativeParsing, $optOff, $disableInnerSpaceRemoval, $disableSpecialEscaping	Accepted, no effect: their BDFD effect on brackets, semicolons and spaces is not reproduced.	Change how the script is read.

Slash commands and moderation

• $message[option] of a user, channel, role or mentionable option returns the ID, not the name. Use $username[...], $channelName[...] or $roleName[...] for the name. $message[1], $message[>] and ranges also work in slash commands (they read the option values in order).
• $banID and $unBanID without an ID are an error in a slash command (Missing or invalid user ID.). The fallback on the last word of the message only exists in prefix commands. IDs must be decimal digits.
• $mentioned returns the command author when nobody is mentioned (historical BDFD default). Write $mentioned[1;no] in guards. Mentions are numbered in the order of the text.
• $kick[], $kick[;reason] and $ban never fall back to the author.
• $customID only exists in the script run for a click (an interactionCreate workflow with customIdFilter), never in the slash command; a button is handled by a workflow.
• $ephemeral and $defer[yes] are decided when the interaction is acknowledged (the engine reads the script first). A script with $newModal, $callWorkflow, $eval or $funcCall is not deferred.
• $channelSendMessage and $sendEmbedMessage only send their own channel message; they do not touch the response being built or its flags ($reply, $ephemeral, $nomention, $dm…). The third argument of $channelSendMessage (message to reply to) is an extension.

Reading the script

• Function names are case-insensitive; temporary variable names are case-sensitive.
• Only \$, \[, \] and \; are escapes. A balanced pair of [ ] inside an argument keeps its content, semicolons included.
• An unknown function is left as text, arguments included (the Manager’s validator reports it as an error).
• Spaces in arguments are kept, not trimmed.
• The whole script is validated before anything runs (arity of every known function, even in a branch not taken).
• A value produced by a variable or an option is never re-read as BDFD. Only $eval[...] evaluates text.

Structures

• $if … $endif is accepted inside the argument of another function. The block closes inside its argument (\; for a literal semicolon). Loops, $try, $jsonForEach and $func are still refused there.
• Conditions: finite decimal numbers are compared exactly as numbers, anything else as text. The operator is searched outside Discord tokens (<@id>, <#id>…). A condition without an operator that is not true or false is an error.
• $async / $endAsync / $await: a block nobody awaits is waited for before the response is sent. 25 blocks per execution.
• Limits: 100,000 steps per execution, 128 nested blocks, a shared time budget per invocation.
• $scriptLanguage always returns BDScript 2.

Extensions

• Autocomplete by script: $appendOptionSuggestion, $autoCompleteOptionName, $autoCompleteOptionValue. The code is stored with the option instead of an $onAutoComplete[Name] callback; 25 suggestions, 2 seconds.
• $modifyChannel: an empty argument leaves the field unchanged; !clear erases the topic.
• $jsonForEach, the 6th argument of $modifyRole (position), and the bdfd.userVariableSemantics setting for user variables.
• $membersCount[Presence] needs the privileged Guild Presence intent.

Some conventions have not been checked against a real BDFD bot (spaces in arguments, empty brackets on $else[], semicolons inside a block in an argument). Do not assume identical behavior for those.