Added, Visual mode: added "Toggle Alpha-based Texture Highlighting" action. When enabled, 3d floor textures and middle textures on double-sided lines will be highlighted only when the crosshair points at a non-transparent pixel.
Changed: multi-part sectors are now better preserved after drawing new lines.
Changed, TEXTURES parser: patch loading errors are now ignored for textures with "NullTexture" option.
Changed, Game configurations: changed default door action arguments to better match vanilla ones.
Fixed, Actions: in some cases keyboard shortcuts involving Ctrl/Alt/Shift modifier keys were displayed incorrectly.
Fixed(?): probably fixed inability to save map wad in Slade 3.
Updated ZDoom_ACS.cfg.
Updated ZDoom_DECORATE.cfg.
Updated ZDoom ACC.

Added, Find and Replace mode: you can now search (and replace) unset sidedef/linedef/thing/sector flags.
Changed, TEXTURES parser: patch loading errors are now treated as warnings for optional textures.
Changed, TEXTURES parser: patch loading is now skipped for textures with "NullTexture" option.

Added Preferences -> Editing -> "Switch view modes when switching to the same Classic Mode" option (disabled by default). When enabled, view mode will be switched between "view floor textures" and "view ceiling textures" when activating the same 2D mode repeatedly.

Added "Next View Mode" and "Previous View Mode" actions.
Removed "Replace unused textures" checkboxes from Edit Linedefs window.
Fixed, SNDINFO parser: commented $ambient sound definitions were treated as editor comments (and still processed).

Changed, Classic modes: displayed mouse map position coordinates are now snapped to current grid size.
Updated model pitch handling to match current GZDoom implementation.
Fixed imprecise vertex coordinates generated by Draw Ellipse mode.
Fixed a resource loading exception when opened map file wad was located in the root of a Directory resource.
Internal: changed output of all InterpolationTools methods from int to float.
Fixed, Internal: InterpolationTools.InterpolateColor() delta usage was inverted.

Added 3 map geometry dragging modes (used when applying Drag Vertices/Linedefs/Sectors modes and Edit Selection mode):
- "Merge Dragged Vertices Only". Only vertex-line intersections will be processed (DB2 mode).
- "Merge Dragged Geometry". Geometry merging will be performed.
- "Replace with Dragged Geometry". Dragged geometry will replace underlaying geometry.
You can switch between these using 3 new actions, top toolbar buttons and Edit menu buttons.
Changed: activating the same 2D mode repeatedly now toggles View modes.
Renamed "Merge Geometry" action/menu item to "Snap to Geometry".
More fixes to vertex/linedef/sector dragging logic.
Updated ZDoom_DECORATE.cfg.

Fixed, ACC compiler: in some cases compilation errors contained map file path as error source instead of lump name when compiling SCRIPTS lump.
Fixed, ACC compiler: in some cases includes were processed incorrectly when compiling external acs files.

Fixed, vertex/linedef/sector dragging: in some cases middle textures were removed from dragged double-sided lines.
Fixed, ACC compiler: fixed a crash when trying to compile SCRIPTS lump of a new map, which wasn't ever saved.

Rewritten vertex/linedef/sector dragging logic. Now it processes line-line intersections. And handles more corner cases. And has less bugs. Probably.
Fixed, Edit Selection mode: texture scale was flipped when "Floor/Ceiling Transform" -> "Scale" was enabled.
Changed: a warning is no longer displayed when trying to compile an empty SCRIPTS lump.
Updated ZDoom_DECORATE.cfg.

Added SNDINFO parser. Currently only the "$ambient" command is parsed. The values are used to update the titles of "Ambient Sound NN" things and to populate "ambient_sounds" Game Configuration enum.
Fixed, DECORATE parser: actors, which used "replaces" keyword and didn't have DoomEdNum were ignored.
Updated documentation ("(G)ZDoom text lumps support" page).

Fixed, Drag Linedefs, Drag Vertices, Edit Selection modes: in some cases sidedefs were incorrectly removed when modifying a closed section of a multi-part sector.
Fixed, Drag Linedefs, Drag Vertices, Drag Sectors, Edit Selection modes: in some cases sidedef textures were not adjusted after applying the modes, leaving middle textures on double-sided lines.

Added, Edit Selection mode: Added "Adjust height" setting. It can be used to adjust floor/ceiling height of selected sectors based on the sector selection was in and the sector selection was moved into.
Removed "Adjust heights to match relatively with surrounding sector" option from Preferences -> Pasting, because sector height adjustments are now handled by Edit Selection mode.
Fixed, Sector info panel: in some cases 0 deg. floor/ceiling texture rotation was triggering texture offset/scale/rotation UI parts to be shown.
Fixed even more cases when sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed, Bridge mode: in some cases calculated floor/ceiling heights were not applied to the sectors created by the mode.
Changed, internal: changed program's CurrentCulture to InvariantCulture.

Changed, internal: made TextLabel and IRenderer2D public properties compatible with DB2 implementation.
Fixed some more cases when sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed, Map Analysis mode: error checks must be updated after switching map format.

Added "safeboundary" game configuration property. The value determines the maximum map bounding box size considered to be safe by "Check map size" error check.
Changed, Map Analysis mode: some checks are now available only under certain conditions (for example, "Check polyobjects" is now available only when the map is in Hexen or UDMF map format).
Updated documentation ("Game Configuration - Basic Settings" page).

Added: sectors are now split into multiple sectors when their shape is divided into several closed shapes by drawing new geometry or dragging existing geometry using Edit Selection and Drag Geometry modes.
Fixed: in some cases sidedefs belonging to linedefs, which were moved on top of existing linedefs, were incorrectly reassigned when applying Edit Selection and Drag Geometry modes.
Fixed: Tag Explorer update fix from R2630 was accidentally placed in an UDMF-only if-block.
Updated ZDoom_DECORATE.cfg (A_WeaponOffset).
Updated documentation ("(G)ZDoom text lumps support" page).

Fixed, Tag Explorer: in some cases (for example, when geometry was removed implicitly by dragging geometry) the list was not updated.
Fixed: in some cases generalized sector effect detection logic failed to detect a valid generalized effect.
Fixed, Action selector control: action label was not updated when changing action number from one generalized effect to another.

Fixed a crash when trying to store a custom field with "Byte Angle" type.
Fixed: in some cases custom field types stored in the map's .dbs file were not applied when loading a map. 

Fixed, Visual mode: texture offsets were updated multiple times when moving texture offsets of several extrafloor sides linked to the same control sidedef.
Fixed, Visual mode: sidedef geometry of sectors affected by "Copy Slope" effect was not updated when the source slope was modified.

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.