Added, Draw Grid mode: "Lock slices to grid" now operates in 4 modes: "None", "Horizontal", "Vertical" and "Both". Can be helpful when drawing ladders and such.
Changed, all drawing modes: changeable drawing mode settings are now persistent.
Changed: "Dynamic grid size" mode is now disabled when changing grid size manually.
Documentation: "Command Line Parameters" topic contained a lot of incorrect information...
Updated ZDoom_DECORATE.cfg.

Fixed, Script Editor: fixed a crash when trying to open Script Editor in a Doom map format map.

Fixed, Custom Fields UI: in some cases mixed user var values were displayed incorrectly.

Fixed, Edit Linedefs window: textures on selected sidedefs must be updated when toggling "Replace unused textures" setting.
Fixed, Texture Selector control: in some cases actual textures were never loaded/displayed when "Replace unused textures" setting was disabled.
Fixed, Script Editor: auto-completion list is no longed displayed when editing comments, includes or strings.

Fixed, Edit Things window: thing type validation when editing multiple thing types was broken in r2527.

Fixed, DECORATE parser: quoted actor string properties (like RenderStyle) were processed incorrectly.
Fixed(?), Update checker: in some cases incorrect update check result was displayed.

Added, Linedef Edit window: added "Replace unused textures" checkbox. When disabled, textures on unused sidedef parts won't be replaced when changing textures. For example, you can now replace sidedef textures of the whole map at once without assigning middle textures to all double-sided sidedefs.
Updated documentation ("Compiling GZDoom Builder" - added "Quick start guide" section).
Updated ZDoom_DECORATE.cfg.

+A couple of cosmetic tweaks and fixes.
Updated ZDoom_DECORATE.cfg.

Fixed, Visual mode: fixed a crash, which happened after these steps: delete things in Classic mode -> undo things deletion in Visual mode -> redo things deletion in Visual mode.

Fixed: checking read-only flag of non-existing files is not a good idea... (fixes a bug introduced in r2520).
Updated ZDoom_DECORATE.cfg (min/max).
Documentation: fixed cosmetic formatting issues in "DECORATE keys" page.

Changed, Action arguments control: arguments are no longer reset to default values when changing action/thing type when old and new argument types and names are the same.

Updated ZDoom_DECORATE.cfg.
Updated documentation ("DECORATE keys" page).

Changed the way filtering in the Edit Things, Browse Action and Browse Effect windows work: items, which names start with filter text are now displayed first.
Cosmetic tweaks to the way thing bounding boxes are rendered in Things mode when "Fixed Things Scale" option is enabled (bounding boxes of highlighted/selected things are now more opaque than the ones of unselected things).
Changed, Preferences form: action selected in the actions list is now stays selected when applying the filtering (unless it's no longer valid).

Fixed, DB2 bug, Visual mode: in some cases (sidedef's sector ceiling lower than other side's sector floor) higher/lower sidedef picking was behaving incorrectly.

Added "Fixed Things Scale" setting (available in the View menu, as a button on the View toolbar and as the "Toggle Fixed Things Scale" action). When enabled, Things will no longer be scaled based on current zoom level in Classic modes, instead, thing bounding box will be drawn when appropriate (this option mimics DB1 things rendering style).
Internal: removed some remnants of fixed rendering pipeline from Renderer2D and Renderer3D.

Fixed, Visual mode: sector geometry was not updated after changing sector brightness under a 3D floor.

Added, DECORATE parser: damage types are now parsed.
Added: the editor now reports duplicate textures/flats/patches/sprites/colormaps/voxels in the loaded wads.
Added, all text parsers: added #region/#endregion support.
Added TERRAIN parser.
Added, Script Editor: added special handling for DECORATE special comments.
Added, Sector Edit window, UDMF: Soundsequence value was setup incorrectly when showing the window for multiple sectors with mixed Soundsequence value. 
Fixed, Map Options window: "Strictly load patches between P_START and P_END" was not applied when applying the changes.
Fixed, MAPINFO parser: MapInfo should be treated as defined when a map MAPINFO block corresponding to current map is encountered even if it doesn't define any properties recognized by the editor.
Fixed, all text parsers: in some cases error line was calculated incorrectly when reporting an error detected by a text parser.
Cosmetic: changed ' to " in the rest of Error and Warning messages.
Internal: added text resource tracking.
Updated ZDoom_DECORATE.cfg.
Updated documentation ("Game Configuration - Basic Settings" page).

Changed, Copy/Paste: the whole pasting operation is now aborted if the resulting number of sectors, linedefs, vertices or things exceeds map format's maximum.

Fixed, Map Options window: game configurations were checked in incorrect order when opening a map without a .dbs file.

Added, "Find Thing Action and Arguments" search mode: "Any action" (-1) can now be used as a search input.
Fixed, "Find Linedef Action and Arguments" and "Find Sector Effect" search modes: in some cases action/effect was checked incorrectly when performing a search. 

Added, "Find Linedef Action and Arguments" search mode: "Any action" (-1) can now be used as a search input.
Added, "Find Sector Effect" search mode: "Any effect" (-1) can now be used as a search input.
Fixed, "Find Linedef Action and Arguments" search mode: generalized actions search was broken.
Fixed, General interface: in some cases the placeholder test engine was displayed in the "Test Map" drop-down.

Added, all drawing modes: added "Continuous drawing" option (available in the top mode menu / Draw Grid panel for the Draw Grid mode). When enabled, drawing mode will not be switched to previously active mode after finishing drawing a shape.
Fixed, general interlace: in some cases "Show Editable Vertices in Visual Mode" top toolbar button showed up when using Doom/Hexen map formats.
Fixed(?), Classic modes: probably fixed an rare issue when map element dragging was not starting when supposed to.

Fixed, General interface, Statistics control: map elements count was displayed incorrectly when the number of map elements was greater than 99999.

Fixed, Texture Browser window: in some cases navigating the textures list using up/down arrows caused an exception.
Fixed, Map Analysis window: fixed an exception on copying warnings to clipboard when the clipboard was used by other application.
Fixed, TEXTURES parser: added special handling for "TNT1A0" sprite name so a texture with this sprite as a single patch is no longer treated as failed loading.
Fixed, Visual mode: in some cases (like line slopes used in several adjacent sectors) sector effect updates were triggered multiple times for the same sector, resulting in noticeable slowdowns and in some cases in infinite recursion.
Updated ZDoom ACC.

Added Preferences -> Interface -> "Keep Filter input focused when image browser is open" option. When enabled, all key presses in image browsers will be redirected to the Filter textbox.
Fixed, Texture Browser: it was impossible to scroll the textures list when selecting textures using the arrow keys.
Fixed, Texture Browser: selecting textures in the textures list using the arrow keys worked differently depending on whether the Filter textbox was focused.
Changed, Texture Browser: the control now tries to select the same item / an item close to the previously selected one when applying filtering to the textures list.

Added, Edit Things window, UDMF: added basic User Variable support. User variables are now automatically shown in the "Custom" tab, are marked with different color and are applied only to actors, which define them.
Fixed, Script Editor: auto-complete can now show the same term several times when it's case is different (like DECORATE's "Bright" keyword and "BRIGHT" flag).
Game configurations, ZDoom: updated "Scroll_Floor" and "Scroll_Ceiling" linedef action argument definitions.
Updated ZDoom_ACS.cfg (Ceiling_CrushAndRaiseSilentDist).
Updated ZDoom_DECORATE.cfg (A_SetChaseThreshold).

Fixed, Tags selector, UDMF: tags from sector with the longest array of tags was applied to sectors with shorter arrays of tags.
Fixed, Draw Settings panel: sidedef texture overrides were not applied when "Auto-clear sidedef textures" setting was enabled.
Added, Thing Edit window, UDMF: added "Show user-added custom fields only" checkbox.

Fixed a case when TEXTRES image was trying to load itself as a patch, which resulted in an infinite loop.
Cosmetic: standardized the way resource names are displayed in warning/error messages in the Errors and Warnings window.

Script Editor, Script Editor configurations: added additional keywords category for properties/operators. Added a separate color for those as well.
Fixed, Script Editor: auto-completion and syntax highlighting now works for properties with dots (like "Powerup.Color") and colon (like "See:").
Fixed, Linedef info panel, Hexen map format, cosmetic: activation type should be enabled when the line has an action assigned, even if it's default activation.
Updated ZDoom_linedefs.cfg (Line_SetPortal).

Re-fixed, Visual mode: in some cases some D3D textures were not disposed after closing a map, eventually resulting in E_OUTOFMEMORY crash.
Fixed, Preferences window: some folding settings were not applied in the Script Editor preview control.
Changed, Visual mode: increased z-buffer depth to 24 bits. Z-fighting among far away but close to each other surfaces should be less noticeable now.

Added, Script Editor: caret position, scroll amount and fold state are now saved for every opened file when closing the Script Editor. Currently selected tab is saved as well.

Fixed, Things mode: Undo for things cloning by Shift-dragging them was created incorrectly (cloned things were moved to their initial position, but not removed).
Fixed, Visual mode: fixed Classic sky texture generation artifact when Bilinear filtering was enabled in Visual mode.
Fixed, Visual mode: fixed Classic sky texture generation artifact when non-power-of-2 Sky textures were used.
Fixed, Visual mode: dynamic lights flickering on surfaces nearly-perpendicular to lights centers should be much harder to trigger now.

Fixed a crash when using "Open map in current WAD" action when trying to reload any ZDoom text lump (as it turned out, implementing IDisposable in ZDTextParser was not such a bright idea...).

Fixed, Script Editor, ACC: auto completion for keywords starting with "#" char was not handled properly.
Fixed, Script Editor: replaced the native Scintilla library with the one supplied with SciTE 3.6.2. The Script Editor should now work on Windows XP.
Changed, Script Editor, search: all fold blocks are now unfolded when search result is inside a folded block.
Updated ZDoom_ACS.cfg.
Updated ZDoom_DECORATE.cfg.
Updated ZDoom ACC to git rev. 6bb023d.