Fixed: MapSet.GetSectorByCoordinates() returned "false" in some cases when a given coordinate was on top of sector's vertex.
Internal: UDMF sector slopes and offsets are no longer stored in sector.Fields. Use sector.FloorSlope, sector.FloorSlopeOffset, sector.CeilingSlope and sector.CeilingSlopeOffset.

Visual mode, 3d floors: fixed broken 3d floor visibility detection (which failed in some cases when real floor or ceiling was sloped).

Tag Range plugin: tags can be set in relative mode (when this mode is enabled, generated values are added to existing tags instead of replacing them).
Updated documentation.

Map Analysis form is now resize-able.
Map Analysis form: number of found errors is now shown in the form's title.

Game Configurations, Error Checker: all blocking things are now checked for being stuck in other things.
Thing Type Info: errorcheck is now set to THING_ERROR_INSIDE_STUCK for blocking DECORATE things.

Tag Selector: tags can now be set relatively using "++N" and "--N" syntax.

ACC: Also updated zdefs.acs and zspecial.acs

Added custom icons for ZDoom's Decal and Sparkle things.

Fixed a typo in the Preferences form.

Linedef Edit Form: fixed a crash when setting a flag to "indeterminate" state when said flag was not present in a linedef's Flags dictionary.
CheckboxArrayControl's OnValueChanged event was not fired if a check-box was in the ThreeState mode.
Minor fixes in the documentation.

Doom_misc.cfg, ZDoom_misc.cfg: changed the highest "sectorbrightness" value to 256 (was 255).

Some game configuration settings were not removed from GZBuilder.cfg after removing them in the Game Configurations form (namely, deletion of texture sets, test engines or linedef color presets was not actually removing them from the config file).

Sector, Linedef, Thing Edit forms: when several map elements are selected, you can set a tag range by entering "++N" or "--N" as a tag.

Thing, Linedef, Sector Edit forms: in some cases flags were set to "enabled" state when they should have been set to "mixed" state when editing multiple map elements.

Sectors mode: things inside of selected sectors can be moved when dragging sectors. This behavior can be toggled by the new button on Sectors mode's toolbar.
Sectors mode: changed Alt-key handling. Now it only enables "snap to grid increment" mode.
Things mode: "snap to grid increment" mode now works in this mode.
Updated documentation.

Visual mode: some parts of 3d floor were shown even when it was above real ceiling/below real floor.
Visual mode: real floor was colored by 3d floor's color even when it was below real floor.
Action Browser form: keyboard focus is now set to Filter text box by default.

MapSet: should probably clamp parsed selection group, because you never know...

Visual mode: unrelated sidedefs were selected when trying to select empty texture using "Select with the same textures" action.

Game Configurations form: game configurations can now be copied and pasted (a context menu is now available in the game configurations list).
Updated documentation.

Rewritten Add to/Select/Clear group Edit menu handling.

Redesigned Texture Set Form a bit.

Updated ZDoom_ACS.cfg and BCC.cfg: more info is now shown in helper popups for all ACS functions (not Action specials). Also, 3 functions (namely SpawnDecal, GetActorPowerupTics and CheckFont) were missing form these configs.
Image Browser control: item selection event was triggered twice.

"Texture 'XXX' is double defined in resource 'YYY'." warning is no longer displayed if a TEXTURE1/2 texture contains a patch with the same name as the texture.  

Script names/numbers cache was not updated (no scripts were shown in the drop downs when using script setting actions).
SCRIPTS lump was not saved when saving a map.

Updated documentation.

"Texture 'XXX' is double defined in resource 'YYY'." warning is no longer displayed if a texture contains a patch with the same name as the texture.  

Classic modes: you can now hold ALT key while dragging map items to lock movement to grid increments relative to initial position.

BCC script compiler (https://github.com/wormt/bcc/) is now bundled with GZDB.
Main Form, "File" menu: only existing files are now added to the "recent files" list.