Added, DECORATE support: #region blocks are now used as thing categories ("//$Category" actor block definition overrides these). Additional category-wide special comments are now available (see documentation).
Updated documentation ("DECORATE keys" page).

Added, Sound Environments mode: sound environments of the same type are now colored using the same color.
Added, Sound Environments mode: current sound environment is now highlighted (can be toggled using "Toggle Highlight" action).
Added: Tag selectors now have up/down buttons.
Fixed, Sound Environments mode: sound environments were not updated after performing Undo/Redo actions.
Fixed, Sound Propagation mode: sound zones were not updated after performing Undo/Redo actions.
Internal: moved "Toggle Highlight" action to the core, also changed it's category to "View".
Internal: "Toggle Highlight" action state is now saved in the Program configuration.
Updated ZDoom_DECORATE.cfg (GetZAt).
Updated ZDoom_linedefs.cfg (Sector_SetPortal args).

Changed, Visual mode: "Auto-align textures" and "Paste Textures Floodfill" actions now use visual mode geometry to determine whether a sidedef part should be processed. This fixes inability to apply said actions to sidedef parts only visible because of slopes.
Fixed, Visual mode: both "With same texture" and "With same height" Select modifiers are now checked when both of them are used at once (previously a sidedef part/floor/ceiling was selected when any of those matched).

Fixed, all drawing modes: in some cases incorrect sector shape was constructed when updating sector shapes after drawing new lines, which resulted in nearby sectors being merged into sector(s) affected by linedefs drawing.

Added: when "sidedefcompressionignoresaction" property is set to false, sidedefs, which belong to a line with a non-zero action or tag, will be skipped when compressing sidedefs.

Fixed, Find and Replace mode: fixed an exception when trying to assemble search result label for a named script without arguments.

Added, Find and Replace mode: action arguments are now displayed in "Linedef Action and Arguments" and "Thing Action and Arguments" search results.

Fixed, Linedefs mode: fixed inability to highlight linedefs when "Stitch geometry within" setting was set to 0.
Fixed, Visual mode: fixed a crash when performing "Auto-align textures" actions on selected sidedefs when there were also floors/ceilings selected.

Game configurations: added "sidedefcompressionignoresaction" property. When set to true, sidedefs will be compressed regardless of linedef action (DB2 behaviour). When set to false, sidedefs, which belong to a line with an action, will be skipped when compressing sidedefs. Default value is false.

Fixed, MODELDEF parser: negative frame number of FrameIndex definition should be treated as "skip model rendering". Also added some more corner case handling.
Fixed, Sound Environment mode: in some cases the view was not updated after updating sound environments.
Added, Sound Environment mode: Sound environment things of currently highlighted sound environment are now highlighted.

Fixed: in some cases sidedefs were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.

Fixed, DECORATE parser: editor comments caused the parser to skip next actor definition when used in incorrect scope.

Fixed, Visual mode: rendering effects of "Slope floor/ceiling to here" things (9500/9501) should not be applied when their arg0 is 0.

Fixed, Visual mode: "Rotate CW"/"Rotate CCW" actions should update thing-based effects when used on Things.
Added/restored, Visual mode: restored "Move Texture Left/Right/Up/Down by 8" actions, added "Move Texture Left/Right/Up/Down by Grid Size" actions (default keys are Ctrl+arrow keys).
Fixed, Game configurations: Hexen's Bell actor was missing "hangs" flag.

Fixed, Script Editor: rewritten keyboard shortcut handling logic. Now it's (hopefully) no longer possible to insert unrelated characters when using keyboard shortcuts. Also "Duplicate line" (Ctrl-D) command was disabled for no reason.

Fixed, Sectors mode: tags and effect labels were displayed instead of selection number labels after disabling, then enabling selection numbers when there were sectors with tags or effects selected.

Fixed, Things mode: fixed a crash when switching to Things mode when more than 256 things were selected.

Added: holding Control key while switching to/from Visual mode will now temporarily disable position synchronization (works only when 'Synchronize camera position between 2D and 3D modes' Preferences option is enabled).
Fixed severe lock-up after finishing dragging many vertices/linedefs/sectors in Classic modes.
Updated documentation ("Synchronizing camera position").

Updated ZDoom_DECORATE.cfg (ALLOWTHRUFLAGS flag).

Fixed, Classic modes: fixed excessive redraws and text label / sector highlight flickering when using rectangular selection with modifier keys.

Fixed, Visual mode: in some cases translucency was ignored on inner top sides of translucent 3d floors.
Internal, Script Editor: moved some setup/auto-completion logic to separate classes.
Updated ZDoom_DECORATE.cfg (A_QuakeEx).

Fixed, Visual mode: 3d floor outer sides were not updated after toggling rendering effects off, then on.
Updated ZDoom_DECORATE.cfg (GetAngle function). 

Fixed, Game configurations window: new test engine entry was still added when pressing "New Test Engine" button, then canceling the browse dialog.
Fixed, general interface: in some cases opening "Test Map" drop-down resulted in an exception when trying to access a disposed/non-existing test engine icon.

Added, Drag Vertices\Linedefs\Sectors\Edit Selection modes: sidedefs facing outside of current selection are now reattached/added/removed after moving the selection.
Currently this will work as intended only if the selection ends up either completely inside a single sector or completely outside of any sector. Also this logic won't be applied if the selection contains the lines with only start or end vertex selected.
Internal: some TextLabel refactoring.

Fixed: added a simple extension-based filtering to Folder/PK3/PK7 resources to prevent loading data from unrelated resources.
Fixed: there can be several entries of the most ZDoom text lumps in WADs. Previously only the first one was processed.
Internal: rewritten DirectoryFilesList to use one collection instead of two.

Added, Sectors, Linedefs, Things modes: map element selection order of rectangular selection is now direction-dependent.

Fixed, Visual mode, UDMF: in some cases Fade color was not applied to floor and ceiling surfaces of 3d floors.
Fixed, Visual mode: in some cases not all sidedef geometry was updated when updating sectors with Plane Align (181) action. Also fixed some more unnecessary geometry updates.
Fixed, Linedefs mode, Things mode: in some cases deleting linedefs/things caused a crash when trying to update text labels.
Fixed, Draw Lines mode: in some cases the drawing was prematurely finished when "Auto-finish drawing" option was enabled.

Added, Draw Lines mode: additional guidelines and horizontal/vertical line lengths can now be displayed for currently drawn line using "Show guidelines" top menu button.
Changed, Draw Lines mode: line angles are now shown only when "Show guidelines" mode is enabled.
Fixed, Draw Lines mode: in some cases "Snap to cardinal directions" mode was snapping only to diagonals.
Fixed, Draw Lines mode: snap to geometry behaved incorrectly when "Snap to cardinal directions" mode was enabled.
Changed, Things mode: dynamic light shape is now drawn using highlight color when a dynamic light thing is highlighted.
Added more sanity checks to MODELDEFS parser.

Added, Visual mode: "Increase/Decrease Scale", "Reset Texture Offsets" and "Reset Local Texture Offsets" actions now work when used on 3d floor sides.
Fixed: CVARINFO parser was unable to parse negative int/float values.
Fixed: in some cases TextLabel text size was checked before it was calculated. 
Internal, Visual mode: reduced the number of unnecessary geometry updates when changing map geometry.
Updated ZDoom_DECORATE.cfg (atan2 and VectorAngle).