Functions pertaining to Real/Fake groups (home realm and instance/battleground-specific groups, respectively) are removed. Instead, group functions take an argument specifying which group you want to query:
LE_PARTY_CATEGORY_HOME will query information about your "real" group -- the group you were in on your Home realm, before entering any instance/battleground.
LE_PARTY_CATEGORY_INSTANCE will query information about your "fake" group -- the group created by the instance/battleground matching mechanism.
Achievement API:
GetAchievementCriteriaInfo split into two separate functions:
GetInstanceInfo - Now returns a MapID as its 8th result, allowing addons to identify the current instance/continent without relying on localized names.
Macros[]
New macro conditionals:
[petbattle]
True when the player is participating in a pet battle.
[possessbar]
[overridebar]
[extrabar]
Talents[]
CHANGED GetTalentInfo - Returns information about talents for player/pet/inspected unit/arbitrary classes.
NEW GetMaxTalentTier - Returns maximum level-appropriate talent tier.
NEW GetTalentRowSelectionInfo - Returns whether a talent is not selected in a given tier, and the selected talent's ID.
NEW LearnTalents - Learns specified talents.
NEW GetTalentClearInfo - Returns information about the cost of unlearning a single talent.
NEW Frame:RegisterUnitEvent("event", "unit1"[, "unit2"]) - Triggers the widget's OnEvent handler when the specified event occurs for the specified units.
NEW Button:SetEnabled(enable) - Enables or disables the widget (available for any widget with Enable/Disable methods).
NEW Region:SetShown(show) - Shows or hides the widget (available for any widget with Show/Hide methods).
FrameXML[]
UIPanelButtonTemplate2 is renamed to UIPanelButtonTemplate; the old version of which is removed.
The minimap buttons MiniMapLFGFrame and MiniMapBattlefieldFrame is renamed/merged to QueueStatusMinimapButton.
ShapeshiftBarFrame is removed; druid shapeshifting UI is now handled by the StanceBarFrame.
Observed bugs and notable differences[]
UnitIsGroupAssistant - the new version of UnitIsRaidOfficer returns false if the player is leader. The old function returned true.
UnitInRange - when not in a party/raid, the new version of UnitInRange returns false for "player" and "pet". The old function returned true.
Texture:SetTexture - If the path passed into Texture:SetTexture(path) is invalid, the texture will display as solid green.
Texture:GetTexture - If the path passed into Texture:SetTexture(path) is invalid, Texture:GetTexture() will still return whatever was passed in. Previously, it would return nil if the texture path was invalid. It seems that it is no longer possible to determine if a texture is valid or not (useful for validating user input).
UnitGUID - requesting the GUID of another party member (possibly raid too - not tested) while responding to the new GROUP_ROSTER_UPDATE event during initial UI load while you are already in a group returns nil. This was not previously the case with the old PARTY_MEMBERS_CHANGED and RAID_ROSTER_UPDATE events.
COMBAT_LOG_EVENT / ENVIRONMENTAL_DAMAGE - the environmental type reported from this event is now reporting non-localized proper case strings (e.g. "Falling") instead of non-localized capitalized strings (e.g. "FALLING").