
LineDefs

+  linedefs without a right side
+  zero length linedefs

+  linedefs which directly overlap (share a pair of vertices)
+  linedefs which partially overlap / cross over  [ties in with unclosed logic]

-  unknown specials

-  one-sided lines without IMPASS flag   [FIX]

-  two-sided lines without 2S flag       [FIX]


Vertices

+  vertices at same location

-  unused vertices  [REMOVE]


Sectors

+  unclosed sectors
+  sectors with ceil_h < floor_h

-  sidedefs used on multiple lines (or same line twice)  [UNPACK]

-  unknown specials

-  unused sectors   [REMOVE]
-  unused sidedefs  [REMOVE]


Things

+  things stuck in walls or each other
-  things in the void
-  unknown things
+  no player 1 start
-  no player 2/3/4 start  (merely show it)
-  no deathmatch starts   (merely show it)


Texturing

-  missing textures on solid walls       [FIX]
-  mid-masked textures on solid walls    [FIX]

-  valid flat names in sectors       [FIX]
-  valid texture names in sidedefs   [FIX]


Tags

-  linedef with tag but no matching sector
-  sector with tag but no matching linedef

-  linedef which requires but lacks a tag

-  teleporter line with missing/multiple target thing.

?  negative tag values

?  list of used tag numbers

